ienumerable - Page 18 - Developer IT

how to print not mapped value

- by IcanMakeIt

I am using complicated SQL queries, i have to use SqlQuery ... in simple way: MODEL: public class C { public int ID { get; set; } [NotMapped] public float Value { get; set; } } CONTROLLER: IEnumerable<C> results = db.C.SqlQuery(@"SELECT ID, ATAN(-45.01) as Value from C); return View(results.ToList()); VIEW: @model IEnumerable<C> @foreach (var item in Model) { @Html.DisplayFor(modelItem => item.Value) } and the result for item.Value is NULL. So my question is , how can i print the computed value from SQL Query ? Thank you for help.

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Resolve property at runtime. C#

- by user1031381

I have some class which have some code public IEnumerable<TypeOne> TypeOne { get { if (db != null) { var col = db.Select<TypeOne>(); if (col.Count > 0) return col; } return db2.TypeOne; } } public IEnumerable<TypeTwo> TypeTwo { get { if (db != null) { var col = db.Select<TypeTwo>(); if (col.Count > 0) return col; } return db2.TypeTwo; } } So as You can see there is a lot of duplicated Code and there are same property name and item type of enumerable. I want to call some property of object like "obj.MyProp". And MyProp must be resolved at runtime with some generic or non-generic method. Is it possible?

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Select a Dictionary<T1, T2> with LINQ

- by Rich

I have used the "select" keyword and extension method to return an IEnumerable<T> with LINQ, but I have a need to return a generic Dictionary<T1, T2> and can't figure it out. The example I learned this from used something in a form similar to the following: IEnumerable<T> coll = from x in y select new SomeClass{ prop1 = value1, prop2 = value2 }; I've also done the same thing with extension methods. I assumed that since the items in a Dictionary<T1, T2> can be iterated as KeyValuePair<T1, T2> that I could just replace "SomeClass" in the above example with "new KeyValuePair<T1, T2> { ...", but that didn't work (Key and Value were marked as readonly, so I could not compile this code). Is this possible, or do I need to do this in multiple steps? Thanks.

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problem with Expression not equal types

- by user428547

class first { private int? firstID; } class second { private int secondID; private int secondField; } public override Expression<Func<first, bool>> FirstFilter() { Contex db = new Contex(); List<second> list = (from p in db.second select p).ToList(); return b => list.Select(p => p.secondID).Contains(b.firstID); } and i have error: cannot convert from 'System.Collections.Generic.IEnumerable' to 'System.Collections.Generic.IEnumerable' i have tried many diferent ways, but i just don't know how can i fix it.

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Creating a dynamic, extensible C# Expando Object

- by Rick Strahl

I love dynamic functionality in a strongly typed language because it offers us the best of both worlds. In C# (or any of the main .NET languages) we now have the dynamic type that provides a host of dynamic features for the static C# language. One place where I've found dynamic to be incredibly useful is in building extensible types or types that expose traditionally non-object data (like dictionaries) in easier to use and more readable syntax. I wrote about a couple of these for accessing old school ADO.NET DataRows and DataReaders more easily for example. These classes are dynamic wrappers that provide easier syntax and auto-type conversions which greatly simplifies code clutter and increases clarity in existing code. ExpandoObject in .NET 4.0 Another great use case for dynamic objects is the ability to create extensible objects - objects that start out with a set of static members and then can add additional properties and even methods dynamically. The .NET 4.0 framework actually includes an ExpandoObject class which provides a very dynamic object that allows you to add properties and methods on the fly and then access them again. For example with ExpandoObject you can do stuff like this:dynamic expand = new ExpandoObject(); expand.Name = "Rick"; expand.HelloWorld = (Func<string, string>) ((string name) => { return "Hello " + name; }); Console.WriteLine(expand.Name); Console.WriteLine(expand.HelloWorld("Dufus")); Internally ExpandoObject uses a Dictionary like structure and interface to store properties and methods and then allows you to add and access properties and methods easily. As cool as ExpandoObject is it has a few shortcomings too: It's a sealed type so you can't use it as a base class It only works off 'properties' in the internal Dictionary - you can't expose existing type data It doesn't serialize to XML or with DataContractSerializer/DataContractJsonSerializer Expando - A truly extensible Object ExpandoObject is nice if you just need a dynamic container for a dictionary like structure. However, if you want to build an extensible object that starts out with a set of strongly typed properties and then allows you to extend it, ExpandoObject does not work because it's a sealed class that can't be inherited. I started thinking about this very scenario for one of my applications I'm building for a customer. In this system we are connecting to various different user stores. Each user store has the same basic requirements for username, password, name etc. But then each store also has a number of extended properties that is available to each application. In the real world scenario the data is loaded from the database in a data reader and the known properties are assigned from the known fields in the database. All unknown fields are then 'added' to the expando object dynamically. In the past I've done this very thing with a separate property - Properties - just like I do for this class. But the property and dictionary syntax is not ideal and tedious to work with. I started thinking about how to represent these extra property structures. One way certainly would be to add a Dictionary, or an ExpandoObject to hold all those extra properties. But wouldn't it be nice if the application could actually extend an existing object that looks something like this as you can with the Expando object:public class User : Westwind.Utilities.Dynamic.Expando { public string Email { get; set; } public string Password { get; set; } public string Name { get; set; } public bool Active { get; set; } public DateTime? ExpiresOn { get; set; } } and then simply start extending the properties of this object dynamically? Using the Expando object I describe later you can now do the following:[TestMethod] public void UserExampleTest() { var user = new User(); // Set strongly typed properties user.Email = "[email protected]"; user.Password = "nonya123"; user.Name = "Rickochet"; user.Active = true; // Now add dynamic properties dynamic duser = user; duser.Entered = DateTime.Now; duser.Accesses = 1; // you can also add dynamic props via indexer user["NickName"] = "AntiSocialX"; duser["WebSite"] = "http://www.west-wind.com/weblog"; // Access strong type through dynamic ref Assert.AreEqual(user.Name,duser.Name); // Access strong type through indexer Assert.AreEqual(user.Password,user["Password"]); // access dyanmically added value through indexer Assert.AreEqual(duser.Entered,user["Entered"]); // access index added value through dynamic Assert.AreEqual(user["NickName"],duser.NickName); // loop through all properties dynamic AND strong type properties (true) foreach (var prop in user.GetProperties(true)) { object val = prop.Value; if (val == null) val = "null"; Console.WriteLine(prop.Key + ": " + val.ToString()); } } As you can see this code somewhat blurs the line between a static and dynamic type. You start with a strongly typed object that has a fixed set of properties. You can then cast the object to dynamic (as I discussed in my last post) and add additional properties to the object. You can also use an indexer to add dynamic properties to the object. To access the strongly typed properties you can use either the strongly typed instance, the indexer or the dynamic cast of the object. Personally I think it's kinda cool to have an easy way to access strongly typed properties by string which can make some data scenarios much easier. To access the 'dynamically added' properties you can use either the indexer on the strongly typed object, or property syntax on the dynamic cast. Using the dynamic type allows all three modes to work on both strongly typed and dynamic properties. Finally you can iterate over all properties, both dynamic and strongly typed if you chose. Lots of flexibility. Note also that by default the Expando object works against the (this) instance meaning it extends the current object. You can also pass in a separate instance to the constructor in which case that object will be used to iterate over to find properties rather than this. Using this approach provides some really interesting functionality when use the dynamic type. To use this we have to add an explicit constructor to the Expando subclass:public class User : Westwind.Utilities.Dynamic.Expando { public string Email { get; set; } public string Password { get; set; } public string Name { get; set; } public bool Active { get; set; } public DateTime? ExpiresOn { get; set; } public User() : base() { } // only required if you want to mix in seperate instance public User(object instance) : base(instance) { } } to allow the instance to be passed. When you do you can now do:[TestMethod] public void ExpandoMixinTest() { // have Expando work on Addresses var user = new User( new Address() ); // cast to dynamicAccessToPropertyTest dynamic duser = user; // Set strongly typed properties duser.Email = "[email protected]"; user.Password = "nonya123"; // Set properties on address object duser.Address = "32 Kaiea"; //duser.Phone = "808-123-2131"; // set dynamic properties duser.NonExistantProperty = "This works too"; // shows default value Address.Phone value Console.WriteLine(duser.Phone); } Using the dynamic cast in this case allows you to access *three* different 'objects': The strong type properties, the dynamically added properties in the dictionary and the properties of the instance passed in! Effectively this gives you a way to simulate multiple inheritance (which is scary - so be very careful with this, but you can do it). How Expando works Behind the scenes Expando is a DynamicObject subclass as I discussed in my last post. By implementing a few of DynamicObject's methods you can basically create a type that can trap 'property missing' and 'method missing' operations. When you access a non-existant property a known method is fired that our code can intercept and provide a value for. Internally Expando uses a custom dictionary implementation to hold the dynamic properties you might add to your expandable object. Let's look at code first. The code for the Expando type is straight forward and given what it provides relatively short. Here it is.using System; using System.Collections.Generic; using System.Linq; using System.Dynamic; using System.Reflection; namespace Westwind.Utilities.Dynamic { /// <summary> /// Class that provides extensible properties and methods. This /// dynamic object stores 'extra' properties in a dictionary or /// checks the actual properties of the instance. /// /// This means you can subclass this expando and retrieve either /// native properties or properties from values in the dictionary. /// /// This type allows you three ways to access its properties: /// /// Directly: any explicitly declared properties are accessible /// Dynamic: dynamic cast allows access to dictionary and native properties/methods /// Dictionary: Any of the extended properties are accessible via IDictionary interface /// </summary> [Serializable] public class Expando : DynamicObject, IDynamicMetaObjectProvider { /// <summary> /// Instance of object passed in /// </summary> object Instance; /// <summary> /// Cached type of the instance /// </summary> Type InstanceType; PropertyInfo[] InstancePropertyInfo { get { if (_InstancePropertyInfo == null && Instance != null) _InstancePropertyInfo = Instance.GetType().GetProperties(BindingFlags.Instance | BindingFlags.Public | BindingFlags.DeclaredOnly); return _InstancePropertyInfo; } } PropertyInfo[] _InstancePropertyInfo; /// <summary> /// String Dictionary that contains the extra dynamic values /// stored on this object/instance /// </summary> /// <remarks>Using PropertyBag to support XML Serialization of the dictionary</remarks> public PropertyBag Properties = new PropertyBag(); //public Dictionary<string,object> Properties = new Dictionary<string, object>(); /// <summary> /// This constructor just works off the internal dictionary and any /// public properties of this object. /// /// Note you can subclass Expando. /// </summary> public Expando() { Initialize(this); } /// <summary> /// Allows passing in an existing instance variable to 'extend'. /// </summary> /// <remarks> /// You can pass in null here if you don't want to /// check native properties and only check the Dictionary! /// </remarks> /// <param name="instance"></param> public Expando(object instance) { Initialize(instance); } protected virtual void Initialize(object instance) { Instance = instance; if (instance != null) InstanceType = instance.GetType(); } /// <summary> /// Try to retrieve a member by name first from instance properties /// followed by the collection entries. /// </summary> /// <param name="binder"></param> /// <param name="result"></param> /// <returns></returns> public override bool TryGetMember(GetMemberBinder binder, out object result) { result = null; // first check the Properties collection for member if (Properties.Keys.Contains(binder.Name)) { result = Properties[binder.Name]; return true; } // Next check for Public properties via Reflection if (Instance != null) { try { return GetProperty(Instance, binder.Name, out result); } catch { } } // failed to retrieve a property result = null; return false; } /// <summary> /// Property setter implementation tries to retrieve value from instance /// first then into this object /// </summary> /// <param name="binder"></param> /// <param name="value"></param> /// <returns></returns> public override bool TrySetMember(SetMemberBinder binder, object value) { // first check to see if there's a native property to set if (Instance != null) { try { bool result = SetProperty(Instance, binder.Name, value); if (result) return true; } catch { } } // no match - set or add to dictionary Properties[binder.Name] = value; return true; } /// <summary> /// Dynamic invocation method. Currently allows only for Reflection based /// operation (no ability to add methods dynamically). /// </summary> /// <param name="binder"></param> /// <param name="args"></param> /// <param name="result"></param> /// <returns></returns> public override bool TryInvokeMember(InvokeMemberBinder binder, object[] args, out object result) { if (Instance != null) { try { // check instance passed in for methods to invoke if (InvokeMethod(Instance, binder.Name, args, out result)) return true; } catch { } } result = null; return false; } /// <summary> /// Reflection Helper method to retrieve a property /// </summary> /// <param name="instance"></param> /// <param name="name"></param> /// <param name="result"></param> /// <returns></returns> protected bool GetProperty(object instance, string name, out object result) { if (instance == null) instance = this; var miArray = InstanceType.GetMember(name, BindingFlags.Public | BindingFlags.GetProperty | BindingFlags.Instance); if (miArray != null && miArray.Length > 0) { var mi = miArray[0]; if (mi.MemberType == MemberTypes.Property) { result = ((PropertyInfo)mi).GetValue(instance,null); return true; } } result = null; return false; } /// <summary> /// Reflection helper method to set a property value /// </summary> /// <param name="instance"></param> /// <param name="name"></param> /// <param name="value"></param> /// <returns></returns> protected bool SetProperty(object instance, string name, object value) { if (instance == null) instance = this; var miArray = InstanceType.GetMember(name, BindingFlags.Public | BindingFlags.SetProperty | BindingFlags.Instance); if (miArray != null && miArray.Length > 0) { var mi = miArray[0]; if (mi.MemberType == MemberTypes.Property) { ((PropertyInfo)mi).SetValue(Instance, value, null); return true; } } return false; } /// <summary> /// Reflection helper method to invoke a method /// </summary> /// <param name="instance"></param> /// <param name="name"></param> /// <param name="args"></param> /// <param name="result"></param> /// <returns></returns> protected bool InvokeMethod(object instance, string name, object[] args, out object result) { if (instance == null) instance = this; // Look at the instanceType var miArray = InstanceType.GetMember(name, BindingFlags.InvokeMethod | BindingFlags.Public | BindingFlags.Instance); if (miArray != null && miArray.Length > 0) { var mi = miArray[0] as MethodInfo; result = mi.Invoke(Instance, args); return true; } result = null; return false; } /// <summary> /// Convenience method that provides a string Indexer /// to the Properties collection AND the strongly typed /// properties of the object by name. /// /// // dynamic /// exp["Address"] = "112 nowhere lane"; /// // strong /// var name = exp["StronglyTypedProperty"] as string; /// </summary> /// <remarks> /// The getter checks the Properties dictionary first /// then looks in PropertyInfo for properties. /// The setter checks the instance properties before /// checking the Properties dictionary. /// </remarks> /// <param name="key"></param> /// /// <returns></returns> public object this[string key] { get { try { // try to get from properties collection first return Properties[key]; } catch (KeyNotFoundException ex) { // try reflection on instanceType object result = null; if (GetProperty(Instance, key, out result)) return result; // nope doesn't exist throw; } } set { if (Properties.ContainsKey(key)) { Properties[key] = value; return; } // check instance for existance of type first var miArray = InstanceType.GetMember(key, BindingFlags.Public | BindingFlags.GetProperty); if (miArray != null && miArray.Length > 0) SetProperty(Instance, key, value); else Properties[key] = value; } } /// <summary> /// Returns and the properties of /// </summary> /// <param name="includeProperties"></param> /// <returns></returns> public IEnumerable<KeyValuePair<string,object>> GetProperties(bool includeInstanceProperties = false) { if (includeInstanceProperties && Instance != null) { foreach (var prop in this.InstancePropertyInfo) yield return new KeyValuePair<string, object>(prop.Name, prop.GetValue(Instance, null)); } foreach (var key in this.Properties.Keys) yield return new KeyValuePair<string, object>(key, this.Properties[key]); } /// <summary> /// Checks whether a property exists in the Property collection /// or as a property on the instance /// </summary> /// <param name="item"></param> /// <returns></returns> public bool Contains(KeyValuePair<string, object> item, bool includeInstanceProperties = false) { bool res = Properties.ContainsKey(item.Key); if (res) return true; if (includeInstanceProperties && Instance != null) { foreach (var prop in this.InstancePropertyInfo) { if (prop.Name == item.Key) return true; } } return false; } } } Although the Expando class supports an indexer, it doesn't actually implement IDictionary or even IEnumerable. It only provides the indexer and Contains() and GetProperties() methods, that work against the Properties dictionary AND the internal instance. The reason for not implementing IDictionary is that a) it doesn't add much value since you can access the Properties dictionary directly and that b) I wanted to keep the interface to class very lean so that it can serve as an entity type if desired. Implementing these IDictionary (or even IEnumerable) causes LINQ extension methods to pop up on the type which obscures the property interface and would only confuse the purpose of the type. IDictionary and IEnumerable are also problematic for XML and JSON Serialization - the XML Serializer doesn't serialize IDictionary<string,object>, nor does the DataContractSerializer. The JavaScriptSerializer does serialize, but it treats the entire object like a dictionary and doesn't serialize the strongly typed properties of the type, only the dictionary values which is also not desirable. Hence the decision to stick with only implementing the indexer to support the user["CustomProperty"] functionality and leaving iteration functions to the publicly exposed Properties dictionary. Note that the Dictionary used here is a custom PropertyBag class I created to allow for serialization to work. One important aspect for my apps is that whatever custom properties get added they have to be accessible to AJAX clients since the particular app I'm working on is a SIngle Page Web app where most of the Web access is through JSON AJAX calls. PropertyBag can serialize to XML and one way serialize to JSON using the JavaScript serializer (not the DCS serializers though). The key components that make Expando work in this code are the Properties Dictionary and the TryGetMember() and TrySetMember() methods. The Properties collection is public so if you choose you can explicitly access the collection to get better performance or to manipulate the members in internal code (like loading up dynamic values form a database). Notice that TryGetMember() and TrySetMember() both work against the dictionary AND the internal instance to retrieve and set properties. This means that user["Name"] works against native properties of the object as does user["Name"] = "RogaDugDog". What's your Use Case? This is still an early prototype but I've plugged it into one of my customer's applications and so far it's working very well. The key features for me were the ability to easily extend the type with values coming from a database and exposing those values in a nice and easy to use manner. I'm also finding that using this type of object for ViewModels works very well to add custom properties to view models. I suspect there will be lots of uses for this - I've been using the extra dictionary approach to extensibility for years - using a dynamic type to make the syntax cleaner is just a bonus here. What can you think of to use this for? Resources Source Code and Tests (GitHub) Also integrated in Westwind.Utilities of the West Wind Web Toolkit West Wind Utilities NuGet© Rick Strahl, West Wind Technologies, 2005-2012Posted in CSharp .NET Dynamic Types Tweet !function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0];if(!d.getElementById(id)){js=d.createElement(s);js.id=id;js.src="//platform.twitter.com/widgets.js";fjs.parentNode.insertBefore(js,fjs);}}(document,"script","twitter-wjs"); (function() { var po = document.createElement('script'); po.type = 'text/javascript'; po.async = true; po.src = 'https://apis.google.com/js/plusone.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(po, s); })();

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Parallelism in .NET – Part 5, Partitioning of Work

- by Reed

When parallelizing any routine, we start by decomposing the problem. Once the problem is understood, we need to break our work into separate tasks, so each task can be run on a different processing element. This process is called partitioning. Partitioning our tasks is a challenging feat. There are opposing forces at work here: too many partitions adds overhead, too few partitions leaves processors idle. Trying to work the perfect balance between the two extremes is the goal for which we should aim. Luckily, the Task Parallel Library automatically handles much of this process. However, there are situations where the default partitioning may not be appropriate, and knowledge of our routines may allow us to guide the framework to making better decisions. First off, I’d like to say that this is a more advanced topic. It is perfectly acceptable to use the parallel constructs in the framework without considering the partitioning taking place. The default behavior in the Task Parallel Library is very well-behaved, even for unusual work loads, and should rarely be adjusted. I have found few situations where the default partitioning behavior in the TPL is not as good or better than my own hand-written partitioning routines, and recommend using the defaults unless there is a strong, measured, and profiled reason to avoid using them. However, understanding partitioning, and how the TPL partitions your data, helps in understanding the proper usage of the TPL. I indirectly mentioned partitioning while discussing aggregation. Typically, our systems will have a limited number of Processing Elements (PE), which is the terminology used for hardware capable of processing a stream of instructions. For example, in a standard Intel i7 system, there are four processor cores, each of which has two potential hardware threads due to Hyperthreading. This gives us a total of 8 PEs – theoretically, we can have up to eight operations occurring concurrently within our system. In order to fully exploit this power, we need to partition our work into Tasks. A task is a simple set of instructions that can be run on a PE. Ideally, we want to have at least one task per PE in the system, since fewer tasks means that some of our processing power will be sitting idle. A naive implementation would be to just take our data, and partition it with one element in our collection being treated as one task. When we loop through our collection in parallel, using this approach, we’d just process one item at a time, then reuse that thread to process the next, etc. There’s a flaw in this approach, however. It will tend to be slower than necessary, often slower than processing the data serially. The problem is that there is overhead associated with each task. When we take a simple foreach loop body and implement it using the TPL, we add overhead. First, we change the body from a simple statement to a delegate, which must be invoked. In order to invoke the delegate on a separate thread, the delegate gets added to the ThreadPool’s current work queue, and the ThreadPool must pull this off the queue, assign it to a free thread, then execute it. If our collection had one million elements, the overhead of trying to spawn one million tasks would destroy our performance. The answer, here, is to partition our collection into groups, and have each group of elements treated as a single task. By adding a partitioning step, we can break our total work into small enough tasks to keep our processors busy, but large enough tasks to avoid overburdening the ThreadPool. There are two clear, opposing goals here: Always try to keep each processor working, but also try to keep the individual partitions as large as possible. When using Parallel.For, the partitioning is always handled automatically. At first, partitioning here seems simple. A naive implementation would merely split the total element count up by the number of PEs in the system, and assign a chunk of data to each processor. Many hand-written partitioning schemes work in this exactly manner. This perfectly balanced, static partitioning scheme works very well if the amount of work is constant for each element. However, this is rarely the case. Often, the length of time required to process an element grows as we progress through the collection, especially if we’re doing numerical computations. In this case, the first PEs will finish early, and sit idle waiting on the last chunks to finish. Sometimes, work can decrease as we progress, since previous computations may be used to speed up later computations. In this situation, the first chunks will be working far longer than the last chunks. In order to balance the workload, many implementations create many small chunks, and reuse threads. This adds overhead, but does provide better load balancing, which in turn improves performance. The Task Parallel Library handles this more elaborately. Chunks are determined at runtime, and start small. They grow slowly over time, getting larger and larger. This tends to lead to a near optimum load balancing, even in odd cases such as increasing or decreasing workloads. Parallel.ForEach is a bit more complicated, however. When working with a generic IEnumerable<T>, the number of items required for processing is not known in advance, and must be discovered at runtime. In addition, since we don’t have direct access to each element, the scheduler must enumerate the collection to process it. Since IEnumerable<T> is not thread safe, it must lock on elements as it enumerates, create temporary collections for each chunk to process, and schedule this out. By default, it uses a partitioning method similar to the one described above. We can see this directly by looking at the Visual Partitioning sample shipped by the Task Parallel Library team, and available as part of the Samples for Parallel Programming. When we run the sample, with four cores and the default, Load Balancing partitioning scheme, we see this: The colored bands represent each processing core. You can see that, when we started (at the top), we begin with very small bands of color. As the routine progresses through the Parallel.ForEach, the chunks get larger and larger (seen by larger and larger stripes). Most of the time, this is fantastic behavior, and most likely will out perform any custom written partitioning. However, if your routine is not scaling well, it may be due to a failure in the default partitioning to handle your specific case. With prior knowledge about your work, it may be possible to partition data more meaningfully than the default Partitioner. There is the option to use an overload of Parallel.ForEach which takes a Partitioner<T> instance. The Partitioner<T> class is an abstract class which allows for both static and dynamic partitioning. By overriding Partitioner<T>.SupportsDynamicPartitions, you can specify whether a dynamic approach is available. If not, your custom Partitioner<T> subclass would override GetPartitions(int), which returns a list of IEnumerator<T> instances. These are then used by the Parallel class to split work up amongst processors. When dynamic partitioning is available, GetDynamicPartitions() is used, which returns an IEnumerable<T> for each partition. If you do decide to implement your own Partitioner<T>, keep in mind the goals and tradeoffs of different partitioning strategies, and design appropriately. The Samples for Parallel Programming project includes a ChunkPartitioner class in the ParallelExtensionsExtras project. This provides example code for implementing your own, custom allocation strategies, including a static allocator of a given chunk size. Although implementing your own Partitioner<T> is possible, as I mentioned above, this is rarely required or useful in practice. The default behavior of the TPL is very good, often better than any hand written partitioning strategy.

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Dynamic Paging and Sorting

- by Ricardo Peres

Since .NET 3.5 brought us LINQ and expressions, I became a great fan of these technologies. There are times, however, when strong typing cannot be used - for example, when you are developing an ObjectDataSource and you need to do paging having just a column name, a page index and a page size, so I set out to fix this. Yes, I know about Dynamic LINQ, and even talked on it previously, but there's no need to add this extra assembly. So, without further delay, here's the code, in both generic and non-generic versions: public static IList ApplyPagingAndSorting(IEnumerable enumerable, Type elementType, Int32 pageSize, Int32 pageIndex, params String [] orderByColumns) { MethodInfo asQueryableMethod = typeof(Queryable).GetMethods(BindingFlags.Static | BindingFlags.Public).Where(m = (m.Name == "AsQueryable") && (m.ContainsGenericParameters == false)).Single(); IQueryable query = (enumerable is IQueryable) ? (enumerable as IQueryable) : asQueryableMethod.Invoke(null, new Object [] { enumerable }) as IQueryable; if ((orderByColumns != null) && (orderByColumns.Length 0)) { PropertyInfo orderByProperty = elementType.GetProperty(orderByColumns [ 0 ]); MemberExpression member = Expression.MakeMemberAccess(Expression.Parameter(elementType, "n"), orderByProperty); LambdaExpression orderBy = Expression.Lambda(member, member.Expression as ParameterExpression); MethodInfo orderByMethod = typeof(Queryable).GetMethods(BindingFlags.Public | BindingFlags.Static).Where(m = m.Name == "OrderBy").ToArray() [ 0 ].MakeGenericMethod(elementType, orderByProperty.PropertyType); query = orderByMethod.Invoke(null, new Object [] { query, orderBy }) as IQueryable; if (orderByColumns.Length 1) { MethodInfo thenByMethod = typeof(Queryable).GetMethods(BindingFlags.Public | BindingFlags.Static).Where(m = m.Name == "ThenBy").ToArray() [ 0 ].MakeGenericMethod(elementType, orderByProperty.PropertyType); PropertyInfo thenByProperty = null; MemberExpression thenByMember = null; LambdaExpression thenBy = null; for (Int32 i = 1; i 0) { MethodInfo takeMethod = typeof(Queryable).GetMethod("Take", BindingFlags.Public | BindingFlags.Static).MakeGenericMethod(elementType); MethodInfo skipMethod = typeof(Queryable).GetMethod("Skip", BindingFlags.Public | BindingFlags.Static).MakeGenericMethod(elementType); query = skipMethod.Invoke(null, new Object [] { query, pageSize * pageIndex }) as IQueryable; query = takeMethod.Invoke(null, new Object [] { query, pageSize }) as IQueryable; } MethodInfo toListMethod = typeof(Enumerable).GetMethod("ToList", BindingFlags.Static | BindingFlags.Public).MakeGenericMethod(elementType); IList list = toListMethod.Invoke(null, new Object [] { query }) as IList; return (list); } public static List ApplyPagingAndSorting(IEnumerable enumerable, Int32 pageSize, Int32 pageIndex, params String [] orderByColumns) { return (ApplyPagingAndSorting(enumerable, typeof(T), pageSize, pageIndex, orderByColumns) as List); } List list = new List { new DateTime(2010, 1, 1), new DateTime(1999, 1, 12), new DateTime(1900, 10, 10), new DateTime(1900, 2, 20), new DateTime(2012, 5, 5), new DateTime(2012, 1, 20) }; List sortedList = ApplyPagingAndSorting(list, 3, 0, "Year", "Month", "Day"); SyntaxHighlighter.config.clipboardSwf = 'http://alexgorbatchev.com/pub/sh/2.0.320/scripts/clipboard.swf'; SyntaxHighlighter.brushes.CSharp.aliases = ['c#', 'c-sharp', 'csharp']; SyntaxHighlighter.all();

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Developing web apps using ASP.NET MVC 3, Razor and EF Code First - Part 1

- by shiju

In this post, I will demonstrate web application development using ASP. NET MVC 3, Razor and EF code First. This post will also cover Dependency Injection using Unity 2.0 and generic Repository and Unit of Work for EF Code First. The following frameworks will be used for this step by step tutorial. ASP.NET MVC 3 EF Code First CTP 5 Unity 2.0 Define Domain Model Let’s create domain model for our simple web application Category class public class Category { public int CategoryId { get; set; } [Required(ErrorMessage = "Name Required")] [StringLength(25, ErrorMessage = "Must be less than 25 characters")] public string Name { get; set;} public string Description { get; set; } public virtual ICollection<Expense> Expenses { get; set; } } Expense class public class Expense { public int ExpenseId { get; set; } public string Transaction { get; set; } public DateTime Date { get; set; } public double Amount { get; set; } public int CategoryId { get; set; } public virtual Category Category { get; set; } } We have two domain entities - Category and Expense. A single category contains a list of expense transactions and every expense transaction should have a Category. In this post, we will be focusing on CRUD operations for the entity Category and will be working on the Expense entity with a View Model object in the later post. And the source code for this application will be refactored over time. The above entities are very simple POCO (Plain Old CLR Object) classes and the entity Category is decorated with validation attributes in the System.ComponentModel.DataAnnotations namespace. Now we want to use these entities for defining model objects for the Entity Framework 4. Using the Code First approach of Entity Framework, we can first define the entities by simply writing POCO classes without any coupling with any API or database library. This approach lets you focus on domain model which will enable Domain-Driven Development for applications. EF code first support is currently enabled with a separate API that is runs on top of the Entity Framework 4. EF Code First is reached CTP 5 when I am writing this article. Creating Context Class for Entity Framework We have created our domain model and let’s create a class in order to working with Entity Framework Code First. For this, you have to download EF Code First CTP 5 and add reference to the assembly EntitFramework.dll. You can also use NuGet to download add reference to EEF Code First. public class MyFinanceContext : DbContext { public MyFinanceContext() : base("MyFinance") { } public DbSet<Category> Categories { get; set; } public DbSet<Expense> Expenses { get; set; } } The above class MyFinanceContext is derived from DbContext that can connect your model classes to a database. The MyFinanceContext class is mapping our Category and Expense class into database tables Categories and Expenses using DbSet<TEntity> where TEntity is any POCO class. When we are running the application at first time, it will automatically create the database. EF code-first look for a connection string in web.config or app.config that has the same name as the dbcontext class. If it is not find any connection string with the convention, it will automatically create database in local SQL Express database by default and the name of the database will be same name as the dbcontext class. You can also define the name of database in constructor of the the dbcontext class. Unlike NHibernate, we don’t have to use any XML based mapping files or Fluent interface for mapping between our model and database. The model classes of Code First are working on the basis of conventions and we can also use a fluent API to refine our model. The convention for primary key is ‘Id’ or ‘<class name>Id’. If primary key properties are detected with type ‘int’, ‘long’ or ‘short’, they will automatically registered as identity columns in the database by default. Primary key detection is not case sensitive. We can define our model classes with validation attributes in the System.ComponentModel.DataAnnotations namespace and it automatically enforces validation rules when a model object is updated or saved. Generic Repository for EF Code First We have created model classes and dbcontext class. Now we have to create generic repository pattern for data persistence with EF code first. If you don’t know about the repository pattern, checkout Martin Fowler’s article on Repository Let’s create a generic repository to working with DbContext and DbSet generics. public interface IRepository<T> where T : class { void Add(T entity); void Delete(T entity); T GetById(long Id); IEnumerable<T> All(); } RepositoryBasse – Generic Repository class public abstract class RepositoryBase<T> where T : class { private MyFinanceContext database; private readonly IDbSet<T> dbset; protected RepositoryBase(IDatabaseFactory databaseFactory) { DatabaseFactory = databaseFactory; dbset = Database.Set<T>(); } protected IDatabaseFactory DatabaseFactory { get; private set; } protected MyFinanceContext Database { get { return database ?? (database = DatabaseFactory.Get()); } } public virtual void Add(T entity) { dbset.Add(entity); } public virtual void Delete(T entity) { dbset.Remove(entity); } public virtual T GetById(long id) { return dbset.Find(id); } public virtual IEnumerable<T> All() { return dbset.ToList(); } } DatabaseFactory class public class DatabaseFactory : Disposable, IDatabaseFactory { private MyFinanceContext database; public MyFinanceContext Get() { return database ?? (database = new MyFinanceContext()); } protected override void DisposeCore() { if (database != null) database.Dispose(); } } Unit of Work If you are new to Unit of Work pattern, checkout Fowler’s article on Unit of Work . According to Martin Fowler, the Unit of Work pattern "maintains a list of objects affected by a business transaction and coordinates the writing out of changes and the resolution of concurrency problems." Let’s create a class for handling Unit of Work public interface IUnitOfWork { void Commit(); } UniOfWork class public class UnitOfWork : IUnitOfWork { private readonly IDatabaseFactory databaseFactory; private MyFinanceContext dataContext; public UnitOfWork(IDatabaseFactory databaseFactory) { this.databaseFactory = databaseFactory; } protected MyFinanceContext DataContext { get { return dataContext ?? (dataContext = databaseFactory.Get()); } } public void Commit() { DataContext.Commit(); } } The Commit method of the UnitOfWork will call the commit method of MyFinanceContext class and it will execute the SaveChanges method of DbContext class. Repository class for Category In this post, we will be focusing on the persistence against Category entity and will working on other entities in later post. Let’s create a repository for handling CRUD operations for Category using derive from a generic Repository RepositoryBase<T>. public class CategoryRepository: RepositoryBase<Category>, ICategoryRepository { public CategoryRepository(IDatabaseFactory databaseFactory) : base(databaseFactory) { } } public interface ICategoryRepository : IRepository<Category> { } If we need additional methods than generic repository for the Category, we can define in the CategoryRepository. Dependency Injection using Unity 2.0 If you are new to Inversion of Control/ Dependency Injection or Unity, please have a look on my articles at http://weblogs.asp.net/shijuvarghese/archive/tags/IoC/default.aspx. I want to create a custom lifetime manager for Unity to store container in the current HttpContext. public class HttpContextLifetimeManager<T> : LifetimeManager, IDisposable { public override object GetValue() { return HttpContext.Current.Items[typeof(T).AssemblyQualifiedName]; } public override void RemoveValue() { HttpContext.Current.Items.Remove(typeof(T).AssemblyQualifiedName); } public override void SetValue(object newValue) { HttpContext.Current.Items[typeof(T).AssemblyQualifiedName] = newValue; } public void Dispose() { RemoveValue(); } } Let’s create controller factory for Unity in the ASP.NET MVC 3 application. public class UnityControllerFactory : DefaultControllerFactory { IUnityContainer container; public UnityControllerFactory(IUnityContainer container) { this.container = container; } protected override IController GetControllerInstance(RequestContext reqContext, Type controllerType) { IController controller; if (controllerType == null) throw new HttpException( 404, String.Format( "The controller for path '{0}' could not be found" + "or it does not implement IController.", reqContext.HttpContext.Request.Path)); if (!typeof(IController).IsAssignableFrom(controllerType)) throw new ArgumentException( string.Format( "Type requested is not a controller: {0}", controllerType.Name), "controllerType"); try { controller= container.Resolve(controllerType) as IController; } catch (Exception ex) { throw new InvalidOperationException(String.Format( "Error resolving controller {0}", controllerType.Name), ex); } return controller; } } Configure contract and concrete types in Unity Let’s configure our contract and concrete types in Unity for resolving our dependencies. private void ConfigureUnity() { //Create UnityContainer IUnityContainer container = new UnityContainer() .RegisterType<IDatabaseFactory, DatabaseFactory>(new HttpContextLifetimeManager<IDatabaseFactory>()) .RegisterType<IUnitOfWork, UnitOfWork>(new HttpContextLifetimeManager<IUnitOfWork>()) .RegisterType<ICategoryRepository, CategoryRepository>(new HttpContextLifetimeManager<ICategoryRepository>()); //Set container for Controller Factory ControllerBuilder.Current.SetControllerFactory( new UnityControllerFactory(container)); } In the above ConfigureUnity method, we are registering our types onto Unity container with custom lifetime manager HttpContextLifetimeManager. Let’s call ConfigureUnity method in the Global.asax.cs for set controller factory for Unity and configuring the types with Unity. protected void Application_Start() { AreaRegistration.RegisterAllAreas(); RegisterGlobalFilters(GlobalFilters.Filters); RegisterRoutes(RouteTable.Routes); ConfigureUnity(); } Developing web application using ASP.NET MVC 3 We have created our domain model for our web application and also have created repositories and configured dependencies with Unity container. Now we have to create controller classes and views for doing CRUD operations against the Category entity. Let’s create controller class for Category Category Controller public class CategoryController : Controller { private readonly ICategoryRepository categoryRepository; private readonly IUnitOfWork unitOfWork; public CategoryController(ICategoryRepository categoryRepository, IUnitOfWork unitOfWork) { this.categoryRepository = categoryRepository; this.unitOfWork = unitOfWork; } public ActionResult Index() { var categories = categoryRepository.All(); return View(categories); } [HttpGet] public ActionResult Edit(int id) { var category = categoryRepository.GetById(id); return View(category); } [HttpPost] public ActionResult Edit(int id, FormCollection collection) { var category = categoryRepository.GetById(id); if (TryUpdateModel(category)) { unitOfWork.Commit(); return RedirectToAction("Index"); } else return View(category); } [HttpGet] public ActionResult Create() { var category = new Category(); return View(category); } [HttpPost] public ActionResult Create(Category category) { if (!ModelState.IsValid) { return View("Create", category); } categoryRepository.Add(category); unitOfWork.Commit(); return RedirectToAction("Index"); } [HttpPost] public ActionResult Delete(int id) { var category = categoryRepository.GetById(id); categoryRepository.Delete(category); unitOfWork.Commit(); var categories = categoryRepository.All(); return PartialView("CategoryList", categories); } } Creating Views in Razor Now we are going to create views in Razor for our ASP.NET MVC 3 application. Let’s create a partial view CategoryList.cshtml for listing category information and providing link for Edit and Delete operations. CategoryList.cshtml @using MyFinance.Helpers; @using MyFinance.Domain; @model IEnumerable<Category> <table> <tr> <th>Actions</th> <th>Name</th> <th>Description</th> </tr> @foreach (var item in Model) { <tr> <td> @Html.ActionLink("Edit", "Edit",new { id = item.CategoryId }) @Ajax.ActionLink("Delete", "Delete", new { id = item.CategoryId }, new AjaxOptions { Confirm = "Delete Expense?", HttpMethod = "Post", UpdateTargetId = "divCategoryList" }) </td> <td> @item.Name </td> <td> @item.Description </td> </tr> } </table> <p> @Html.ActionLink("Create New", "Create") </p> The delete link is providing Ajax functionality using the Ajax.ActionLink. This will call an Ajax request for Delete action method in the CategoryCotroller class. In the Delete action method, it will return Partial View CategoryList after deleting the record. We are using CategoryList view for the Ajax functionality and also for Index view using for displaying list of category information. Let’s create Index view using partial view CategoryList Index.chtml @model IEnumerable<MyFinance.Domain.Category> @{ ViewBag.Title = "Index"; } <h2>Category List</h2> <script src="@Url.Content("~/Scripts/jquery.unobtrusive-ajax.min.js")" type="text/javascript"></script> <div id="divCategoryList"> @Html.Partial("CategoryList", Model) </div> We can call the partial views using Html.Partial helper method. Now we are going to create View pages for insert and update functionality for the Category. Both view pages are sharing common user interface for entering the category information. So I want to create an EditorTemplate for the Category information. We have to create the EditorTemplate with the same name of entity object so that we can refer it on view pages using @Html.EditorFor(model => model) . So let’s create template with name Category. Let’s create view page for insert Category information @model MyFinance.Domain.Category @{ ViewBag.Title = "Save"; } <h2>Create</h2> <script src="@Url.Content("~/Scripts/jquery.validate.min.js")" type="text/javascript"></script> <script src="@Url.Content("~/Scripts/jquery.validate.unobtrusive.min.js")" type="text/javascript"></script> @using (Html.BeginForm()) { @Html.ValidationSummary(true) <fieldset> <legend>Category</legend> @Html.EditorFor(model => model) <p> <input type="submit" value="Create" /> </p> </fieldset> } <div> @Html.ActionLink("Back to List", "Index") </div> ViewStart file In Razor views, we can add a file named _viewstart.cshtml in the views directory and this will be shared among the all views with in the Views directory. The below code in the _viewstart.cshtml, sets the Layout page for every Views in the Views folder. @{ Layout = "~/Views/Shared/_Layout.cshtml"; } Source Code You can download the source code from http://efmvc.codeplex.com/ . The source will be refactored on over time. Summary In this post, we have created a simple web application using ASP.NET MVC 3 and EF Code First. We have discussed on technologies and practices such as ASP.NET MVC 3, Razor, EF Code First, Unity 2, generic Repository and Unit of Work. In my later posts, I will modify the application and will be discussed on more things. Stay tuned to my blog for more posts on step by step application building.

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NoSQL with RavenDB and ASP.NET MVC - Part 2

- by shiju

In my previous post, we have discussed on how to work with RavenDB document database in an ASP.NET MVC application. We have setup RavenDB for our ASP.NET MVC application and did basic CRUD operations against a simple domain entity. In this post, let’s discuss on domain entity with deep object graph and how to query against RavenDB documents using Indexes.Let's create two domain entities for our demo ASP.NET MVC appplication public class Category { public string Id { get; set; } [Required(ErrorMessage = "Name Required")] [StringLength(25, ErrorMessage = "Must be less than 25 characters")] public string Name { get; set;} public string Description { get; set; } public List<Expense> Expenses { get; set; } public Category() { Expenses = new List<Expense>(); } } public class Expense { public string Id { get; set; } public Category Category { get; set; } public string Transaction { get; set; } public DateTime Date { get; set; } public double Amount { get; set; } } We have two domain entities - Category and Expense. A single category contains a list of expense transactions and every expense transaction should have a Category.Let's create ASP.NET MVC view model for Expense transaction public class ExpenseViewModel { public string Id { get; set; } public string CategoryId { get; set; } [Required(ErrorMessage = "Transaction Required")] public string Transaction { get; set; } [Required(ErrorMessage = "Date Required")] public DateTime Date { get; set; } [Required(ErrorMessage = "Amount Required")] public double Amount { get; set; } public IEnumerable<SelectListItem> Category { get; set; } } Let's create a contract type for Expense Repository public interface IExpenseRepository { Expense Load(string id); IEnumerable<Expense> GetExpenseTransactions(DateTime startDate,DateTime endDate); void Save(Expense expense,string categoryId); void Delete(string id); } Let's create a concrete type for Expense Repository for handling CRUD operations. public class ExpenseRepository : IExpenseRepository { private IDocumentSession session; public ExpenseRepository() { session = MvcApplication.CurrentSession; } public Expense Load(string id) { return session.Load<Expense>(id); } public IEnumerable<Expense> GetExpenseTransactions(DateTime startDate, DateTime endDate) { //Querying using the Index name "ExpenseTransactions" //filtering with dates var expenses = session.LuceneQuery<Expense>("ExpenseTransactions") .WaitForNonStaleResults() .Where(exp => exp.Date >= startDate && exp.Date <= endDate) .ToArray(); return expenses; } public void Save(Expense expense,string categoryId) { var category = session.Load<Category>(categoryId); if (string.IsNullOrEmpty(expense.Id)) { //new expense transaction expense.Category = category; session.Store(expense); } else { //modifying an existing expense transaction var expenseToEdit = Load(expense.Id); //Copy values to expenseToEdit ModelCopier.CopyModel(expense, expenseToEdit); //set category object expenseToEdit.Category = category; } //save changes session.SaveChanges(); } public void Delete(string id) { var expense = Load(id); session.Delete<Expense>(expense); session.SaveChanges(); } } Insert/Update Expense Transaction The Save method is used for both insert a new expense record and modifying an existing expense transaction. For a new expense transaction, we store the expense object with associated category into document session object and load the existing expense object and assign values to it for editing a existing record. public void Save(Expense expense,string categoryId) { var category = session.Load<Category>(categoryId); if (string.IsNullOrEmpty(expense.Id)) { //new expense transaction expense.Category = category; session.Store(expense); } else { //modifying an existing expense transaction var expenseToEdit = Load(expense.Id); //Copy values to expenseToEdit ModelCopier.CopyModel(expense, expenseToEdit); //set category object expenseToEdit.Category = category; } //save changes session.SaveChanges(); } Querying Expense transactions public IEnumerable<Expense> GetExpenseTransactions(DateTime startDate, DateTime endDate) { //Querying using the Index name "ExpenseTransactions" //filtering with dates var expenses = session.LuceneQuery<Expense>("ExpenseTransactions") .WaitForNonStaleResults() .Where(exp => exp.Date >= startDate && exp.Date <= endDate) .ToArray(); return expenses; } The GetExpenseTransactions method returns expense transactions using a LINQ query expression with a Date comparison filter. The Lucene Query is using a index named "ExpenseTransactions" for getting the result set. In RavenDB, Indexes are LINQ queries stored in the RavenDB server and would be executed on the background and will perform query against the JSON documents. Indexes will be working with a lucene query expression or a set operation. Indexes are composed using a Map and Reduce function. Check out Ayende's blog post on Map/Reduce We can create index using RavenDB web admin tool as well as programmitically using its Client API. The below shows the screen shot of creating index using web admin tool. We can also create Indexes using Raven Cleint API as shown in the following code documentStore.DatabaseCommands.PutIndex("ExpenseTransactions", new IndexDefinition<Expense,Expense>() { Map = Expenses => from exp in Expenses select new { exp.Date } }); In the Map function, we used a Linq expression as shown in the following from exp in docs.Expensesselect new { exp.Date };We have not used a Reduce function for the above index. A Reduce function is useful while performing aggregate functions based on the results from the Map function. Indexes can be use with set operations of RavenDB.SET OperationsUnlike other document databases, RavenDB supports set based operations that lets you to perform updates, deletes and inserts to the bulk_docs endpoint of RavenDB. For doing this, you just pass a query to a Index as shown in the following commandDELETE http://localhost:8080/bulk_docs/ExpenseTransactions?query=Date:20100531The above command using the Index named "ExpenseTransactions" for querying the documents with Date filter and will delete all the documents that match the query criteria. The above command is equivalent of the following queryDELETE FROM ExpensesWHERE Date='2010-05-31' Controller & ActionsWe have created Expense Repository class for performing CRUD operations for the Expense transactions. Let's create a controller class for handling expense transactions. public class ExpenseController : Controller { private ICategoryRepository categoyRepository; private IExpenseRepository expenseRepository; public ExpenseController(ICategoryRepository categoyRepository, IExpenseRepository expenseRepository) { this.categoyRepository = categoyRepository; this.expenseRepository = expenseRepository; } //Get Expense transactions based on dates public ActionResult Index(DateTime? StartDate, DateTime? EndDate) { //If date is not passed, take current month's first and last dte DateTime dtNow; dtNow = DateTime.Today; if (!StartDate.HasValue) { StartDate = new DateTime(dtNow.Year, dtNow.Month, 1); EndDate = StartDate.Value.AddMonths(1).AddDays(-1); } //take last date of startdate's month, if endate is not passed if (StartDate.HasValue && !EndDate.HasValue) { EndDate = (new DateTime(StartDate.Value.Year, StartDate.Value.Month, 1)).AddMonths(1).AddDays(-1); } var expenses = expenseRepository.GetExpenseTransactions(StartDate.Value, EndDate.Value); if (Request.IsAjaxRequest()) { return PartialView("ExpenseList", expenses); } ViewData.Add("StartDate", StartDate.Value.ToShortDateString()); ViewData.Add("EndDate", EndDate.Value.ToShortDateString()); return View(expenses); } // GET: /Expense/Edit public ActionResult Edit(string id) { var expenseModel = new ExpenseViewModel(); var expense = expenseRepository.Load(id); ModelCopier.CopyModel(expense, expenseModel); var categories = categoyRepository.GetCategories(); expenseModel.Category = categories.ToSelectListItems(expense.Category.Id.ToString()); return View("Save", expenseModel); } // // GET: /Expense/Create public ActionResult Create() { var expenseModel = new ExpenseViewModel(); var categories = categoyRepository.GetCategories(); expenseModel.Category = categories.ToSelectListItems("-1"); expenseModel.Date = DateTime.Today; return View("Save", expenseModel); } // // POST: /Expense/Save // Insert/Update Expense Tansaction [HttpPost] public ActionResult Save(ExpenseViewModel expenseViewModel) { try { if (!ModelState.IsValid) { var categories = categoyRepository.GetCategories(); expenseViewModel.Category = categories.ToSelectListItems(expenseViewModel.CategoryId); return View("Save", expenseViewModel); } var expense=new Expense(); ModelCopier.CopyModel(expenseViewModel, expense); expenseRepository.Save(expense, expenseViewModel.CategoryId); return RedirectToAction("Index"); } catch { return View(); } } //Delete a Expense Transaction public ActionResult Delete(string id) { expenseRepository.Delete(id); return RedirectToAction("Index"); } } Download the Source - You can download the source code from http://ravenmvc.codeplex.com

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Chunking a List - .NET vs Python

- by Abhijeet Patel

Chunking a List As I mentioned last time, I'm knee deep in python these days. I come from a statically typed background so it's definitely a mental adjustment. List comprehensions is BIG in Python and having worked with a few of them I can see why. Let's say we need to chunk a list into sublists of a specified size. Here is how we'd do it in C# static class Extensions { public static IEnumerable<List<T>> Chunk<T>(this List<T> l, int chunkSize) { if (chunkSize <0) { throw new ArgumentException("chunkSize cannot be negative", "chunkSize"); } for (int i = 0; i < l.Count; i += chunkSize) { yield return new List<T>(l.Skip(i).Take(chunkSize)); } } } static void Main(string[] args) { var l = new List<string> { "a", "b", "c", "d", "e", "f","g" }; foreach (var list in l.Chunk(7)) { string str = list.Aggregate((s1, s2) => s1 + "," + s2); Console.WriteLine(str); } } A little wordy but still pretty concise thanks to LINQ.We skip the iteration number plus chunkSize elements and yield out a new List of chunkSize elements on each iteration. The python implementation is a bit more terse. def chunkIterable(iter, chunkSize): '''Chunks an iterable object into a list of the specified chunkSize ''' assert hasattr(iter, "__iter__"), "iter is not an iterable" for i in xrange(0, len(iter), chunkSize): yield iter[i:i + chunkSize] if __name__ == '__main__': l = ['a', 'b', 'c', 'd', 'e', 'f'] generator = chunkIterable(l,2) try: while(1): print generator.next() except StopIteration: pass xrange generates elements in the specified range taking in a seed and returning a generator. which can be used in a for loop(much like using a C# iterator in a foreach loop) Since chunkIterable has a yield statement, it turns this method into a generator as well. iter[i:i + chunkSize] essentially slices the list based on the current iteration index and chunksize and creates a new list that we yield out to the caller one at a time. A generator much like an iterator is a state machine and each subsequent call to it remembers the state at which the last call left off and resumes execution from that point. The caveat to keep in mind is that since variables are not explicitly typed we need to ensure that the object passed in is iterable using hasattr(iter, "__iter__").This way we can perform chunking on any object which is an "iterable", very similar to accepting an IEnumerable in the .NET land

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ANTS CLR and Memory Profiler In Depth Review (Part 1 of 2 – CLR Profiler)

- by ToStringTheory

One of the things that people might not know about me, is my obsession to make my code as efficient as possible. Many people might not realize how much of a task or undertaking that this might be, but it is surely a task as monumental as climbing Mount Everest, except this time it is a challenge for the mind… In trying to make code efficient, there are many different factors that play a part – size of project or solution, tiers, language used, experience and training of the programmer, technologies used, maintainability of the code – the list can go on for quite some time. I spend quite a bit of time when developing trying to determine what is the best way to implement a feature to accomplish the efficiency that I look to achieve. One program that I have recently come to learn about – Red Gate ANTS Performance (CLR) and Memory profiler gives me tools to accomplish that job more efficiently as well. In this review, I am going to cover some of the features of the ANTS profiler set by compiling some hideous example code to test against. Notice As a member of the Geeks With Blogs Influencers program, one of the perks is the ability to review products, in exchange for a free license to the program. I have not let this affect my opinions of the product in any way, and Red Gate nor Geeks With Blogs has tried to influence my opinion regarding this product in any way. Introduction The ANTS Profiler pack provided by Red Gate was something that I had not heard of before receiving an email regarding an offer to review it for a license. Since I look to make my code efficient, it was a no brainer for me to try it out! One thing that I have to say took me by surprise is that upon downloading the program and installing it you fill out a form for your usual contact information. Sure enough within 2 hours, I received an email from a sales representative at Red Gate asking if she could help me to achieve the most out of my trial time so it wouldn’t go to waste. After replying to her and explaining that I was looking to review its feature set, she put me in contact with someone that setup a demo session to give me a quick rundown of its features via an online meeting. After having dealt with a massive ordeal with one of my utility companies and their complete lack of customer service, Red Gates friendly and helpful representatives were a breath of fresh air, and something I was thankful for. ANTS CLR Profiler The ANTS CLR profiler is the thing I want to focus on the most in this post, so I am going to dive right in now. Install was simple and took no time at all. It installed both the profiler for the CLR and Memory, but also visual studio extensions to facilitate the usage of the profilers (click any images for full size images): The Visual Studio menu options (under ANTS menu) Starting the CLR Performance Profiler from the start menu yields this window If you follow the instructions after launching the program from the start menu (Click File > New Profiling Session to start a new project), you are given a dialog with plenty of options for profiling: The New Session dialog. Lots of options. One thing I noticed is that the buttons in the lower right were half-covered by the panel of the application. If I had to guess, I would imagine that this is caused by my DPI settings being set to 125%. This is a problem I have seen in other applications as well that don’t scale well to different dpi scales. The profiler options give you the ability to profile: .NET Executable ASP.NET web application (hosted in IIS) ASP.NET web application (hosted in IIS express) ASP.NET web application (hosted in Cassini Web Development Server) SharePoint web application (hosted in IIS) Silverlight 4+ application Windows Service COM+ server XBAP (local XAML browser application) Attach to an already running .NET 4 process Choosing each option provides a varying set of other variables/options that one can set including options such as application arguments, operating path, record I/O performance performance counters to record (43 counters in all!), etc… All in all, they give you the ability to profile many different .Net project types, and make it simple to do so. In most cases of my using this application, I would be using the built in Visual Studio extensions, as they automatically start a new profiling project in ANTS with the options setup, and start your program, however RedGate has made it easy enough to profile outside of Visual Studio as well. On the flip side of this, as someone who lives most of their work life in Visual Studio, one thing I do wish is that instead of opening an entirely separate application/gui to perform profiling after launching, that instead they would provide a Visual Studio panel with the information, and integrate more of the profiling project information into Visual Studio. So, now that we have an idea of what options that the profiler gives us, its time to test its abilities and features. Horrendous Example Code – Prime Number Generator One of my interests besides development, is Physics and Math – what I went to college for. I have especially always been interested in prime numbers, as they are something of a mystery… So, I decided that I would go ahead and to test the abilities of the profiler, I would write a small program, website, and library to generate prime numbers in the quantity that you ask for. I am going to start off with some terrible code, and show how I would see the profiler being used as a development tool. First off, the IPrimes interface (all code is downloadable at the end of the post): interface IPrimes { IEnumerable<int> GetPrimes(int retrieve); } Simple enough, right? Anything that implements the interface will (hopefully) provide an IEnumerable of int, with the quantity specified in the parameter argument. Next, I am going to implement this interface in the most basic way: public class DumbPrimes : IPrimes { public IEnumerable<int> GetPrimes(int retrieve) { //store a list of primes already found var _foundPrimes = new List<int>() { 2, 3 }; //if i ask for 1 or two primes, return what asked for if (retrieve <= _foundPrimes.Count()) return _foundPrimes.Take(retrieve); //the next number to look at int _analyzing = 4; //since I already determined I don't have enough //execute at least once, and until quantity is sufficed do { //assume prime until otherwise determined bool isPrime = true; //start dividing at 2 //divide until number is reached, or determined not prime for (int i = 2; i < _analyzing && isPrime; i++) { //if (i) goes into _analyzing without a remainder, //_analyzing is NOT prime if (_analyzing % i == 0) isPrime = false; } //if it is prime, add to found list if (isPrime) _foundPrimes.Add(_analyzing); //increment number to analyze next _analyzing++; } while (_foundPrimes.Count() < retrieve); return _foundPrimes; } } This is the simplest way to get primes in my opinion. Checking each number by the straight definition of a prime – is it divisible by anything besides 1 and itself. I have included this code in a base class library for my solution, as I am going to use it to demonstrate a couple of features of ANTS. This class library is consumed by a simple non-MVVM WPF application, and a simple MVC4 website. I will not post the WPF code here inline, as it is simply an ObservableCollection<int>, a label, two textbox’s, and a button. Starting a new Profiling Session So, in Visual Studio, I have just completed my first stint developing the GUI and DumbPrimes IPrimes class, so now I want to check my codes efficiency by profiling it. All I have to do is build the solution (surprised initiating a profiling session doesn’t do this, but I suppose I can understand it), and then click the ANTS menu, followed by Profile Performance. I am then greeted by the profiler starting up and already monitoring my program live: You are provided with a realtime graph at the top, and a pane at the bottom giving you information on how to proceed. I am going to start by asking my program to show me the first 15000 primes: After the program finally began responding again (I did all the work on the main UI thread – how bad!), I stopped the profiler, which did kill the process of my program too. One important thing to note, is that the profiler by default wants to give you a lot of detail about the operation – line hit counts, time per line, percent time per line, etc… The important thing to remember is that this itself takes a lot of time. When running my program without the profiler attached, it can generate the 15000 primes in 5.18 seconds, compared to 74.5 seconds – almost a 1500 percent increase. While this may seem like a lot, remember that there is a trade off. It may be WAY more inefficient, however, I am able to drill down and make improvements to specific problem areas, and then decrease execution time all around. Analyzing the Profiling Session After clicking ‘Stop Profiling’, the process running my application stopped, and the entire execution time was automatically selected by ANTS, and the results shown below: Now there are a number of interesting things going on here, I am going to cover each in a section of its own: Real Time Performance Counter Bar (top of screen) At the top of the screen, is the real time performance bar. As your application is running, this will constantly update with the currently selected performance counters status. A couple of cool things to note are the fact that you can drag a selection around specific time periods to drill down the detail views in the lower 2 panels to information pertaining to only that period. After selecting a time period, you can bookmark a section and name it, so that it is easy to find later, or after reloaded at a later time. You can also zoom in, out, or fit the graph to the space provided – useful for drilling down. It may be hard to see, but at the top of the processor time graph below the time ticks, but above the red usage graph, there is a green bar. This bar shows at what times a method that is selected in the ‘Call tree’ panel is called. Very cool to be able to click on a method and see at what times it made an impact. As I said before, ANTS provides 43 different performance counters you can hook into. Click the arrow next to the Performance tab at the top will allow you to change between different counters if you have them selected: Method Call Tree, ADO.Net Database Calls, File IO – Detail Panel Red Gate really hit the mark here I think. When you select a section of the run with the graph, the call tree populates to fill a hierarchical tree of method calls, with information regarding each of the methods. By default, methods are hidden where the source is not provided (framework type code), however, Red Gate has integrated Reflector into ANTS, so even if you don’t have source for something, you can select a method and get the source if you want. Methods are also hidden where the impact is seen as insignificant – methods that are only executed for 1% of the time of the overall calling methods time; in other words, working on making them better is not where your efforts should be focused. – Smart! Source Panel – Detail Panel The source panel is where you can see line level information on your code, showing the code for the currently selected method from the Method Call Tree. If the code is not available, Reflector takes care of it and shows the code anyways! As you can notice, there does seem to be a problem with how ANTS determines what line is the actual line that a call is completed on. I have suspicions that this may be due to some of the inline code optimizations that the CLR applies upon compilation of the assembly. In a method with comments, the problem is much more severe: As you can see here, apparently the most offending code in my base library was a comment – *gasp*! Removing the comments does help quite a bit, however I hope that Red Gate works on their counter algorithm soon to improve the logic on positioning for statistics: I did a small test just to demonstrate the lines are correct without comments. For me, it isn’t a deal breaker, as I can usually determine the correct placements by looking at the application code in the region and determining what makes sense, but it is something that would probably build up some irritation with time. Feature – Suggest Method for Optimization A neat feature to really help those in need of a pointer, is the menu option under tools to automatically suggest methods to optimize/improve: Nice feature – clicking it filters the call tree and stars methods that it thinks are good candidates for optimization. I do wish that they would have made it more visible for those of use who aren’t great on sight: Process Integration I do think that this could have a place in my process. After experimenting with the profiler, I do think it would be a great benefit to do some development, testing, and then after all the bugs are worked out, use the profiler to check on things to make sure nothing seems like it is hogging more than its fair share. For example, with this program, I would have developed it, ran it, tested it – it works, but slowly. After looking at the profiler, and seeing the massive amount of time spent in 1 method, I might go ahead and try to re-implement IPrimes (I actually would probably rewrite the offending code, but so that I can distribute both sets of code easily, I’m just going to make another implementation of IPrimes). Using two pieces of knowledge about prime numbers can make this method MUCH more efficient – prime numbers fall into two buckets 6k+/-1 , and a number is prime if it is not divisible by any other primes before it: public class SmartPrimes : IPrimes { public IEnumerable<int> GetPrimes(int retrieve) { //store a list of primes already found var _foundPrimes = new List<int>() { 2, 3 }; //if i ask for 1 or two primes, return what asked for if (retrieve <= _foundPrimes.Count()) return _foundPrimes.Take(retrieve); //the next number to look at int _k = 1; //since I already determined I don't have enough //execute at least once, and until quantity is sufficed do { //assume prime until otherwise determined bool isPrime = true; int potentialPrime; //analyze 6k-1 //assign the value to potential potentialPrime = 6 * _k - 1; //if there are any primes that divise this, it is NOT a prime number //using PLINQ for quick boost isPrime = !_foundPrimes.AsParallel() .Any(prime => potentialPrime % prime == 0); //if it is prime, add to found list if (isPrime) _foundPrimes.Add(potentialPrime); if (_foundPrimes.Count() == retrieve) break; //analyze 6k+1 //assign the value to potential potentialPrime = 6 * _k + 1; //if there are any primes that divise this, it is NOT a prime number //using PLINQ for quick boost isPrime = !_foundPrimes.AsParallel() .Any(prime => potentialPrime % prime == 0); //if it is prime, add to found list if (isPrime) _foundPrimes.Add(potentialPrime); //increment k to analyze next _k++; } while (_foundPrimes.Count() < retrieve); return _foundPrimes; } } Now there are definitely more things I can do to help make this more efficient, but for the scope of this example, I think this is fine (but still hideous)! Profiling this now yields a happy surprise 27 seconds to generate the 15000 primes with the profiler attached, and only 1.43 seconds without. One important thing I wanted to call out though was the performance graph now: Notice anything odd? The %Processor time is above 100%. This is because there is now more than 1 core in the operation. A better label for the chart in my mind would have been %Core time, but to each their own. Another odd thing I noticed was that the profiler seemed to be spot on this time in my DumbPrimes class with line details in source, even with comments.. Odd. Profiling Web Applications The last thing that I wanted to cover, that means a lot to me as a web developer, is the great amount of work that Red Gate put into the profiler when profiling web applications. In my solution, I have a simple MVC4 application setup with 1 page, a single input form, that will output prime values as my WPF app did. Launching the profiler from Visual Studio as before, nothing is really different in the profiler window, however I did receive a UAC prompt for a Red Gate helper app to integrate with the web server without notification. After requesting 500, 1000, 2000, and 5000 primes, and looking at the profiler session, things are slightly different from before: As you can see, there are 4 spikes of activity in the processor time graph, but there is also something new in the call tree: That’s right – ANTS will actually group method calls by get/post operations, so it is easier to find out what action/page is giving the largest problems… Pretty cool in my mind! Overview Overall, I think that Red Gate ANTS CLR Profiler has a lot to offer, however I think it also has a long ways to go. 3 Biggest Pros: Ability to easily drill down from time graph, to method calls, to source code Wide variety of counters to choose from when profiling your application Excellent integration/grouping of methods being called from web applications by request – BRILLIANT! 3 Biggest Cons: Issue regarding line details in source view Nit pick – Processor time vs. Core time Nit pick – Lack of full integration with Visual Studio Ratings Ease of Use (7/10) – I marked down here because of the problems with the line level details and the extra work that that entails, and the lack of better integration with Visual Studio. Effectiveness (10/10) – I believe that the profiler does EXACTLY what it purports to do. Especially with its large variety of performance counters, a definite plus! Features (9/10) – Besides the real time performance monitoring, and the drill downs that I’ve shown here, ANTS also has great integration with ADO.Net, with the ability to show database queries run by your application in the profiler. This, with the line level details, the web request grouping, reflector integration, and various options to customize your profiling session I think create a great set of features! Customer Service (10/10) – My entire experience with Red Gate personnel has been nothing but good. their people are friendly, helpful, and happy! UI / UX (8/10) – The interface is very easy to get around, and all of the options are easy to find. With a little bit of poking around, you’ll be optimizing Hello World in no time flat! Overall (8/10) – Overall, I am happy with the Performance Profiler and its features, as well as with the service I received when working with the Red Gate personnel. I WOULD recommend you trying the application and seeing if it would fit into your process, BUT, remember there are still some kinks in it to hopefully be worked out. My next post will definitely be shorter (hopefully), but thank you for reading up to here, or skipping ahead! Please, if you do try the product, drop me a message and let me know what you think! I would love to hear any opinions you may have on the product. Code Feel free to download the code I used above – download via DropBox

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C#: Does an IDisposable in a Halted Iterator Dispose?

- by James Michael Hare

If that sounds confusing, let me give you an example. Let's say you expose a method to read a database of products, and instead of returning a List<Product> you return an IEnumerable<Product> in iterator form (yield return). This accomplishes several good things: The IDataReader is not passed out of the Data Access Layer which prevents abstraction leak and resource leak potentials. You don't need to construct a full List<Product> in memory (which could be very big) if you just want to forward iterate once. If you only want to consume up to a certain point in the list, you won't incur the database cost of looking up the other items. This could give us an example like: 1: // a sample data access object class to do standard CRUD operations. 2: public class ProductDao 3: { 4: private DbProviderFactory _factory = SqlClientFactory.Instance 5: 6: // a method that would retrieve all available products 7: public IEnumerable<Product> GetAvailableProducts() 8: { 9: // must create the connection 10: using (var con = _factory.CreateConnection()) 11: { 12: con.ConnectionString = _productsConnectionString; 13: con.Open(); 14: 15: // create the command 16: using (var cmd = _factory.CreateCommand()) 17: { 18: cmd.Connection = con; 19: cmd.CommandText = _getAllProductsStoredProc; 20: cmd.CommandType = CommandType.StoredProcedure; 21: 22: // get a reader and pass back all results 23: using (var reader = cmd.ExecuteReader()) 24: { 25: while(reader.Read()) 26: { 27: yield return new Product 28: { 29: Name = reader["product_name"].ToString(), 30: ... 31: }; 32: } 33: } 34: } 35: } 36: } 37: } The database details themselves are irrelevant. I will say, though, that I'm a big fan of using the System.Data.Common classes instead of your provider specific counterparts directly (SqlCommand, OracleCommand, etc). This lets you mock your data sources easily in unit testing and also allows you to swap out your provider in one line of code. In fact, one of the shared components I'm most proud of implementing was our group's DatabaseUtility library that simplifies all the database access above into one line of code in a thread-safe and provider-neutral way. I went with my own flavor instead of the EL due to the fact I didn't want to force internal company consumers to use the EL if they didn't want to, and it made it easy to allow them to mock their database for unit testing by providing a MockCommand, MockConnection, etc that followed the System.Data.Common model. One of these days I'll blog on that if anyone's interested. Regardless, you often have situations like the above where you are consuming and iterating through a resource that must be closed once you are finished iterating. For the reasons stated above, I didn't want to return IDataReader (that would force them to remember to Dispose it), and I didn't want to return List<Product> (that would force them to hold all products in memory) -- but the first time I wrote this, I was worried. What if you never consume the last item and exit the loop? Are the reader, command, and connection all disposed correctly? Of course, I was 99.999999% sure the creators of C# had already thought of this and taken care of it, but inspection in Reflector was difficult due to the nature of the state machines yield return generates, so I decided to try a quick example program to verify whether or not Dispose() will be called when an iterator is broken from outside the iterator itself -- i.e. before the iterator reports there are no more items. So I wrote a quick Sequencer class with a Dispose() method and an iterator for it. Yes, it is COMPLETELY contrived: 1: // A disposable sequence of int -- yes this is completely contrived... 2: internal class Sequencer : IDisposable 3: { 4: private int _i = 0; 5: private readonly object _mutex = new object(); 6: 7: // Constructs an int sequence. 8: public Sequencer(int start) 9: { 10: _i = start; 11: } 12: 13: // Gets the next integer 14: public int GetNext() 15: { 16: lock (_mutex) 17: { 18: return _i++; 19: } 20: } 21: 22: // Dispose the sequence of integers. 23: public void Dispose() 24: { 25: // force output immediately (flush the buffer) 26: Console.WriteLine("Disposed with last sequence number of {0}!", _i); 27: Console.Out.Flush(); 28: } 29: } And then I created a generator (infinite-loop iterator) that did the using block for auto-Disposal: 1: // simply defines an extension method off of an int to start a sequence 2: public static class SequencerExtensions 3: { 4: // generates an infinite sequence starting at the specified number 5: public static IEnumerable<int> GetSequence(this int starter) 6: { 7: // note the using here, will call Dispose() when block terminated. 8: using (var seq = new Sequencer(starter)) 9: { 10: // infinite loop on this generator, means must be bounded by caller! 11: while(true) 12: { 13: yield return seq.GetNext(); 14: } 15: } 16: } 17: } This is really the same conundrum as the database problem originally posed. Here we are using iteration (yield return) over a large collection (infinite sequence of integers). If we cut the sequence short by breaking iteration, will that using block exit and hence, Dispose be called? Well, let's see: 1: // The test program class 2: public class IteratorTest 3: { 4: // The main test method. 5: public static void Main() 6: { 7: Console.WriteLine("Going to consume 10 of infinite items"); 8: Console.Out.Flush(); 9: 10: foreach(var i in 0.GetSequence()) 11: { 12: // could use TakeWhile, but wanted to output right at break... 13: if(i >= 10) 14: { 15: Console.WriteLine("Breaking now!"); 16: Console.Out.Flush(); 17: break; 18: } 19: 20: Console.WriteLine(i); 21: Console.Out.Flush(); 22: } 23: 24: Console.WriteLine("Done with loop."); 25: Console.Out.Flush(); 26: } 27: } So, what do we see? Do we see the "Disposed" message from our dispose, or did the Dispose get skipped because from an "eyeball" perspective we should be locked in that infinite generator loop? Here's the results: 1: Going to consume 10 of infinite items 2: 0 3: 1 4: 2 5: 3 6: 4 7: 5 8: 6 9: 7 10: 8 11: 9 12: Breaking now! 13: Disposed with last sequence number of 11! 14: Done with loop. Yes indeed, when we break the loop, the state machine that C# generates for yield iterate exits the iteration through the using blocks and auto-disposes the IDisposable correctly. I must admit, though, the first time I wrote one, I began to wonder and that led to this test. If you've never seen iterators before (I wrote a previous entry here) the infinite loop may throw you, but you have to keep in mind it is not a linear piece of code, that every time you hit a "yield return" it cedes control back to the state machine generated for the iterator. And this state machine, I'm happy to say, is smart enough to clean up the using blocks correctly. I suspected those wily guys and gals at Microsoft engineered it well, and I wasn't disappointed. But, I've been bitten by assumptions before, so it's good to test and see. Yes, maybe you knew it would or figured it would, but isn't it nice to know? And as those campy 80s G.I. Joe cartoon public service reminders always taught us, "Knowing is half the battle...". Technorati Tags: C#,.NET

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NHibernate Error - Expression argument must be of type ICollection

- by Liam McLennan

The above error occurred when I executed a linq query using the following expression: (s) => s.Book.Slug.Equals(bookslug) && ids.Contains(s.Id); ids in this case is of type IEnumerable<Guid>. As indicated by the error message the fix is to change ids to ICollection<Guid>, then the query executes successfully.

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Crazy Linq: performing System.ComponentModel.DataAnnotations validation in a single statement

- by Daniel Cazzulino

public static IEnumerable<ValidationResult> Validate(object component) { return from descriptor in TypeDescriptor.GetProperties(component).Cast<PropertyDescriptor>() from validation in descriptor.Attributes.OfType<System.ComponentModel.DataAnnotations.ValidationAttribute>() where !validation.IsValid(descriptor.GetValue(component)) select new ValidationResult( validation.ErrorMessage ?? string.Format(CultureInfo.CurrentUICulture, "{0} validation failed.", validation.GetType().Name), new[] { descriptor.Name }); } ...Read full article

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Dynamic Filtering

- by Ricardo Peres

Continuing my previous posts on dynamic LINQ, now it's time for dynamic filtering. For now, I'll focus on string matching. There are three standard operators for string matching, which both NHibernate, Entity Framework and LINQ to SQL recognize: Equals Contains StartsWith EndsWith So, if we want to apply filtering by one of these operators on a string property, we can use this code: public enum MatchType { StartsWith = 0, EndsWith = 1, Contains = 2, Equals = 3 } public static List Filter(IEnumerable enumerable, String propertyName, String filter, MatchType matchType) { return (Filter(enumerable, typeof(T), propertyName, filter, matchType) as List); } public static IList Filter(IEnumerable enumerable, Type elementType, String propertyName, String filter, MatchType matchType) { MethodInfo asQueryableMethod = typeof(Queryable).GetMethods(BindingFlags.Static | BindingFlags.Public).Where(m = (m.Name == "AsQueryable") && (m.ContainsGenericParameters == false)).Single(); IQueryable query = (enumerable is IQueryable) ? (enumerable as IQueryable) : asQueryableMethod.Invoke(null, new Object [] { enumerable }) as IQueryable; MethodInfo whereMethod = typeof(Queryable).GetMethods(BindingFlags.Public | BindingFlags.Static).Where(m = m.Name == "Where").ToArray() [ 0 ].MakeGenericMethod(elementType); MethodInfo matchMethod = typeof(String).GetMethod ( (matchType == MatchType.StartsWith) ? "StartsWith" : (matchType == MatchType.EndsWith) ? "EndsWith" : (matchType == MatchType.Contains) ? "Contains" : "Equals", new Type [] { typeof(String) } ); PropertyInfo displayProperty = elementType.GetProperty(propertyName, BindingFlags.Public | BindingFlags.Instance); MemberExpression member = Expression.MakeMemberAccess(Expression.Parameter(elementType, "n"), displayProperty); MethodCallExpression call = Expression.Call(member, matchMethod, Expression.Constant(filter)); LambdaExpression where = Expression.Lambda(call, member.Expression as ParameterExpression); query = whereMethod.Invoke(null, new Object [] { query, where }) as IQueryable; MethodInfo toListMethod = typeof(Enumerable).GetMethod("ToList", BindingFlags.Static | BindingFlags.Public).MakeGenericMethod(elementType); IList list = toListMethod.Invoke(null, new Object [] { query }) as IList; return (list); } var list = new [] { new { A = "aa" }, new { A = "aabb" }, new { A = "ccaa" }, new { A = "ddaadd" } }; var contains = Filter(list, "A", "aa", MatchType.Contains); var endsWith = Filter(list, "A", "aa", MatchType.EndsWith); var startsWith = Filter(list, "A", "aa", MatchType.StartsWith); var equals = Filter(list, "A", "aa", MatchType.Equals); Perhaps I'll write some more posts on this subject in the near future. SyntaxHighlighter.config.clipboardSwf = 'http://alexgorbatchev.com/pub/sh/2.0.320/scripts/clipboard.swf'; SyntaxHighlighter.brushes.CSharp.aliases = ['c#', 'c-sharp', 'csharp']; SyntaxHighlighter.all();

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LINQ: Enhancing Distinct With The SelectorEqualityComparer

- by Paulo Morgado

On my last post, I introduced the PredicateEqualityComparer and a Distinct extension method that receives a predicate to internally create a PredicateEqualityComparer to filter elements. Using the predicate, greatly improves readability, conciseness and expressiveness of the queries, but it can be even better. Most of the times, we don’t want to provide a comparison method but just to extract the comaprison key for the elements. So, I developed a SelectorEqualityComparer that takes a method that extracts the key value for each element. Something like this: public class SelectorEqualityComparer<TSource, Tkey> : EqualityComparer<TSource> where Tkey : IEquatable<Tkey> { private Func<TSource, Tkey> selector; public SelectorEqualityComparer(Func<TSource, Tkey> selector) : base() { this.selector = selector; } public override bool Equals(TSource x, TSource y) { Tkey xKey = this.GetKey(x); Tkey yKey = this.GetKey(y); if (xKey != null) { return ((yKey != null) && xKey.Equals(yKey)); } return (yKey == null); } public override int GetHashCode(TSource obj) { Tkey key = this.GetKey(obj); return (key == null) ? 0 : key.GetHashCode(); } public override bool Equals(object obj) { SelectorEqualityComparer<TSource, Tkey> comparer = obj as SelectorEqualityComparer<TSource, Tkey>; return (comparer != null); } public override int GetHashCode() { return base.GetType().Name.GetHashCode(); } private Tkey GetKey(TSource obj) { return (obj == null) ? (Tkey)(object)null : this.selector(obj); } } Now I can write code like this: .Distinct(new SelectorEqualityComparer<Source, Key>(x => x.Field)) And, for improved readability, conciseness and expressiveness and support for anonymous types the corresponding Distinct extension method: public static IEnumerable<TSource> Distinct<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> selector) where TKey : IEquatable<TKey> { return source.Distinct(new SelectorEqualityComparer<TSource, TKey>(selector)); } And the query is now written like this: .Distinct(x => x.Field) For most usages, it’s simpler than using a predicate.

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Compare Two NameValueCollections Extension Method

- by Jon Canning

public static class NameValueCollectionExtension { public static bool CollectionEquals(this NameValueCollection nameValueCollection1, NameValueCollection nameValueCollection2) { return nameValueCollection1.ToKeyValue().SequenceEqual(nameValueCollection2.ToKeyValue()); } private static IEnumerable<object> ToKeyValue(this NameValueCollection nameValueCollection) { return nameValueCollection.AllKeys.OrderBy(x => x).Select(x => new {Key = x, Value = nameValueCollection[x]}); } }

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Entity Framework 5, separating business logic from model - Repository?

- by bnice7

I am working on my first public-facing web application and I’m using MVC 4 for the presentation layer and EF 5 for the DAL. The database structure is locked, and there are moderate differences between how the user inputs data and how the database itself gets populated. I have done a ton of reading on the repository pattern (which I have never used) but most of my research is pushing me away from using it since it supposedly creates an unnecessary level of abstraction for the latest versions of EF since repositories and unit-of-work are already built-in. My initial approach is to simply create a separate set of classes for my business objects in the BLL that can act as an intermediary between my Controllers and the DAL. Here’s an example class: public class MyBuilding { public int Id { get; private set; } public string Name { get; set; } public string Notes { get; set; } private readonly Entities _context = new Entities(); // Is this thread safe? private static readonly int UserId = WebSecurity.GetCurrentUser().UserId; public IEnumerable<MyBuilding> GetList() { IEnumerable<MyBuilding> buildingList = from p in _context.BuildingInfo where p.Building.UserProfile.UserId == UserId select new MyBuilding {Id = p.BuildingId, Name = p.BuildingName, Notes = p.Building.Notes}; return buildingList; } public void Create() { var b = new Building {UserId = UserId, Notes = this.Notes}; _context.Building.Add(b); _context.SaveChanges(); // Set the building ID this.Id = b.BuildingId; // Seed 1-to-1 tables with reference the new building _context.BuildingInfo.Add(new BuildingInfo {Building = b}); _context.GeneralInfo.Add(new GeneralInfo {Building = b}); _context.LocationInfo.Add(new LocationInfo {Building = b}); _context.SaveChanges(); } public static MyBuilding Find(int id) { using (var context = new Entities()) // Is this OK to do in a static method? { var b = context.Building.FirstOrDefault(p => p.BuildingId == id && p.UserId == UserId); if (b == null) throw new Exception("Error: Building not found or user does not have access."); return new MyBuilding {Id = b.BuildingId, Name = b.BuildingInfo.BuildingName, Notes = b.Notes}; } } } My primary concern: Is the way I am instantiating my DbContext as a private property thread-safe, and is it safe to have a static method that instantiates a separate DbContext? Or am I approaching this all wrong? I am not opposed to learning up on the repository pattern if I am taking the total wrong approach here.

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What is the abstract name for Drive, Directory and file?

- by Omkar panhalkar

I want to give nice name to my function while returns drive, directory and file. Can you please suggest a good abstract name for this trio? This is the function. static IEnumerable<string> GetDriveDirectoriesAndFile(string path) { if (path.Contains('/')) { path = path.Replace('/', '\\'); } if (path.Contains('\\')) { return path.Split('\\'); } return null; } Thanks, Omkar

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What are the best practices to use NHiberante sessions in asp.net (mvc/web api) ?

- by mrt181

I have the following setup in my project: public class WebApiApplication : System.Web.HttpApplication { public static ISessionFactory SessionFactory { get; private set; } public WebApiApplication() { this.BeginRequest += delegate { var session = SessionFactory.OpenSession(); CurrentSessionContext.Bind(session); }; this.EndRequest += delegate { var session = SessionFactory.GetCurrentSession(); if (session == null) { return; } session = CurrentSessionContext.Unbind(SessionFactory); session.Dispose(); }; } protected void Application_Start() { AreaRegistration.RegisterAllAreas(); FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters); RouteConfig.RegisterRoutes(RouteTable.Routes); BundleConfig.RegisterBundles(BundleTable.Bundles); var assembly = Assembly.GetCallingAssembly(); SessionFactory = new NHibernateHelper(assembly, Server.MapPath("/")).SessionFactory; } } public class PositionsController : ApiController { private readonly ISession session; public PositionsController() { this.session = WebApiApplication.SessionFactory.GetCurrentSession(); } public IEnumerable<Position> Get() { var result = this.session.Query<Position>().Cacheable().ToList(); if (!result.Any()) { throw new HttpResponseException(new HttpResponseMessage(HttpStatusCode.NotFound)); } return result; } public HttpResponseMessage Post(PositionDataTransfer dto) { //TODO: Map dto to model IEnumerable<Position> positions = null; using (var transaction = this.session.BeginTransaction()) { this.session.SaveOrUpdate(positions); try { transaction.Commit(); } catch (StaleObjectStateException) { if (transaction != null && transaction.IsActive) { transaction.Rollback(); } } } var response = this.Request.CreateResponse(HttpStatusCode.Created, dto); response.Headers.Location = new Uri(this.Request.RequestUri.AbsoluteUri + "/" + dto.Name); return response; } public void Put(int id, string value) { //TODO: Implement PUT throw new NotImplementedException(); } public void Delete(int id) { //TODO: Implement DELETE throw new NotImplementedException(); } } I am not sure if this is the recommended way to insert the session into the controller. I was thinking about using DI but i am not sure how to inject the session that is opened and binded in the BeginRequest delegate into the Controllers constructor to get this public PositionsController(ISession session) { this.session = session; } Question: What is the recommended way to use NHiberante sessions in asp.net mvc/web api ?

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NHibernate Conventions

- by Ricardo Peres

Introduction It seems that nowadays everyone loves conventions! Not the ones that you go to, but the ones that you use, that is! It just happens that NHibernate also supports conventions, and we’ll see exactly how. Conventions in NHibernate are supported in two ways: Naming of tables and columns when not explicitly indicated in the mappings; Full domain mapping. Naming of Tables and Columns Since always NHibernate has supported the concept of a naming strategy. A naming strategy in NHibernate converts class and property names to table and column names and vice-versa, when a name is not explicitly supplied. In concrete, it must be a realization of the NHibernate.Cfg.INamingStrategy interface, of which NHibernate includes two implementations: DefaultNamingStrategy: the default implementation, where each column and table are mapped to identically named properties and classes, for example, “MyEntity” will translate to “MyEntity”; ImprovedNamingStrategy: underscores (_) are used to separate Pascal-cased fragments, for example, entity “MyEntity” will be mapped to a “my_entity” table. The naming strategy can be defined at configuration level (the Configuration instance) by calling the SetNamingStrategy method: 1: cfg.SetNamingStrategy(ImprovedNamingStrategy.Instance); Both the DefaultNamingStrategy and the ImprovedNamingStrategy classes offer singleton instances in the form of Instance static fields. DefaultNamingStrategy is the one NHibernate uses, if you don’t specify one. Domain Mapping In mapping by code, we have the choice of relying on conventions to do the mapping automatically. This means a class will inspect our classes and decide how they will relate to the database objects. The class that handles conventions is NHibernate.Mapping.ByCode.ConventionModelMapper, a specialization of the base by code mapper, NHibernate.Mapping.ByCode.ModelMapper. The ModelMapper relies on an internal SimpleModelInspector to help it decide what and how to map, but the mapper lets you override its decisions. You apply code conventions like this: 1: //pick the types that you want to map 2: IEnumerable<Type> types = Assembly.GetExecutingAssembly().GetExportedTypes(); 3: 4: //conventions based mapper 5: ConventionModelMapper mapper = new ConventionModelMapper(); 6: 7: HbmMapping mapping = mapper.CompileMappingFor(types); 8: 9: //the one and only configuration instance 10: Configuration cfg = ...; 11: cfg.AddMapping(mapping); This is a very simple example, it lacks, at least, the id generation strategy, which you can add by adding an event handler like this: 1: mapper.BeforeMapClass += (IModelInspector modelInspector, Type type, IClassAttributesMapper classCustomizer) => 2: { 3: classCustomizer.Id(x => 4: { 5: //set the hilo generator 6: x.Generator(Generators.HighLow); 7: }); 8: }; The mapper will fire events like this whenever it needs to get information about what to do. And basically this is all it takes to automatically map your domain! It will correctly configure many-to-one and one-to-many relations, choosing bags or sets depending on your collections, will get the table and column names from the naming strategy we saw earlier and will apply the usual defaults to all properties, such as laziness and fetch mode. However, there is at least one thing missing: many-to-many relations. The conventional mapper doesn’t know how to find and configure them, which is a pity, but, alas, not difficult to overcome. To start, for my projects, I have this rule: each entity exposes a public property of type ISet<T> where T is, of course, the type of the other endpoint entity. Extensible as it is, NHibernate lets me implement this very easily: 1: mapper.IsOneToMany((MemberInfo member, Boolean isLikely) => 2: { 3: Type sourceType = member.DeclaringType; 4: Type destinationType = member.GetMemberFromDeclaringType().GetPropertyOrFieldType(); 5: 6: //check if the property is of a generic collection type 7: if ((destinationType.IsGenericCollection() == true) && (destinationType.GetGenericArguments().Length == 1)) 8: { 9: Type destinationEntityType = destinationType.GetGenericArguments().Single(); 10: 11: //check if the type of the generic collection property is an entity 12: if (mapper.ModelInspector.IsEntity(destinationEntityType) == true) 13: { 14: //check if there is an equivalent property on the target type that is also a generic collection and points to this entity 15: PropertyInfo collectionInDestinationType = destinationEntityType.GetProperties().Where(x => (x.PropertyType.IsGenericCollection() == true) && (x.PropertyType.GetGenericArguments().Length == 1) && (x.PropertyType.GetGenericArguments().Single() == sourceType)).SingleOrDefault(); 16: 17: if (collectionInDestinationType != null) 18: { 19: return (false); 20: } 21: } 22: } 23: 24: return (true); 25: }); 26: 27: mapper.IsManyToMany((MemberInfo member, Boolean isLikely) => 28: { 29: //a relation is many to many if it isn't one to many 30: Boolean isOneToMany = mapper.ModelInspector.IsOneToMany(member); 31: return (!isOneToMany); 32: }); 33: 34: mapper.BeforeMapManyToMany += (IModelInspector modelInspector, PropertyPath member, IManyToManyMapper collectionRelationManyToManyCustomizer) => 35: { 36: Type destinationEntityType = member.LocalMember.GetPropertyOrFieldType().GetGenericArguments().First(); 37: //set the mapping table column names from each source entity name plus the _Id sufix 38: collectionRelationManyToManyCustomizer.Column(destinationEntityType.Name + "_Id"); 39: }; 40: 41: mapper.BeforeMapSet += (IModelInspector modelInspector, PropertyPath member, ISetPropertiesMapper propertyCustomizer) => 42: { 43: if (modelInspector.IsManyToMany(member.LocalMember) == true) 44: { 45: propertyCustomizer.Key(x => x.Column(member.LocalMember.DeclaringType.Name + "_Id")); 46: 47: Type sourceType = member.LocalMember.DeclaringType; 48: Type destinationType = member.LocalMember.GetPropertyOrFieldType().GetGenericArguments().First(); 49: IEnumerable<String> names = new Type[] { sourceType, destinationType }.Select(x => x.Name).OrderBy(x => x); 50: 51: //set inverse on the relation of the alphabetically first entity name 52: propertyCustomizer.Inverse(sourceType.Name == names.First()); 53: //set mapping table name from the entity names in alphabetical order 54: propertyCustomizer.Table(String.Join("_", names)); 55: } 56: }; We have to understand how the conventions mapper thinks: For each collection of entities found, it will ask the mapper if it is a one-to-many; in our case, if the collection is a generic one that has an entity as its generic parameter, and the generic parameter type has a similar collection, then it is not a one-to-many; Next, the mapper will ask if the collection that it now knows is not a one-to-many is a many-to-many; Before a set is mapped, if it corresponds to a many-to-many, we set its mapping table. Now, this is tricky: because we have no way to maintain state, we sort the names of the two endpoint entities and we combine them with a “_”; for the first alphabetical entity, we set its relation to inverse – remember, on a many-to-many relation, only one endpoint must be marked as inverse; finally, we set the column name as the name of the entity with an “_Id” suffix; Before the many-to-many relation is processed, we set the column name as the name of the other endpoint entity with the “_Id” suffix, as we did for the set. And that’s it. With these rules, NHibernate will now happily find and configure many-to-many relations, as well as all the others. You can wrap this in a new conventions mapper class, so that it is more easily reusable: 1: public class ManyToManyConventionModelMapper : ConventionModelMapper 2: { 3: public ManyToManyConventionModelMapper() 4: { 5: base.IsOneToMany((MemberInfo member, Boolean isLikely) => 6: { 7: return (this.IsOneToMany(member, isLikely)); 8: }); 9: 10: base.IsManyToMany((MemberInfo member, Boolean isLikely) => 11: { 12: return (this.IsManyToMany(member, isLikely)); 13: }); 14: 15: base.BeforeMapManyToMany += this.BeforeMapManyToMany; 16: base.BeforeMapSet += this.BeforeMapSet; 17: } 18: 19: protected virtual Boolean IsManyToMany(MemberInfo member, Boolean isLikely) 20: { 21: //a relation is many to many if it isn't one to many 22: Boolean isOneToMany = this.ModelInspector.IsOneToMany(member); 23: return (!isOneToMany); 24: } 25: 26: protected virtual Boolean IsOneToMany(MemberInfo member, Boolean isLikely) 27: { 28: Type sourceType = member.DeclaringType; 29: Type destinationType = member.GetMemberFromDeclaringType().GetPropertyOrFieldType(); 30: 31: //check if the property is of a generic collection type 32: if ((destinationType.IsGenericCollection() == true) && (destinationType.GetGenericArguments().Length == 1)) 33: { 34: Type destinationEntityType = destinationType.GetGenericArguments().Single(); 35: 36: //check if the type of the generic collection property is an entity 37: if (this.ModelInspector.IsEntity(destinationEntityType) == true) 38: { 39: //check if there is an equivalent property on the target type that is also a generic collection and points to this entity 40: PropertyInfo collectionInDestinationType = destinationEntityType.GetProperties().Where(x => (x.PropertyType.IsGenericCollection() == true) && (x.PropertyType.GetGenericArguments().Length == 1) && (x.PropertyType.GetGenericArguments().Single() == sourceType)).SingleOrDefault(); 41: 42: if (collectionInDestinationType != null) 43: { 44: return (false); 45: } 46: } 47: } 48: 49: return (true); 50: } 51: 52: protected virtual new void BeforeMapManyToMany(IModelInspector modelInspector, PropertyPath member, IManyToManyMapper collectionRelationManyToManyCustomizer) 53: { 54: Type destinationEntityType = member.LocalMember.GetPropertyOrFieldType().GetGenericArguments().First(); 55: //set the mapping table column names from each source entity name plus the _Id sufix 56: collectionRelationManyToManyCustomizer.Column(destinationEntityType.Name + "_Id"); 57: } 58: 59: protected virtual new void BeforeMapSet(IModelInspector modelInspector, PropertyPath member, ISetPropertiesMapper propertyCustomizer) 60: { 61: if (modelInspector.IsManyToMany(member.LocalMember) == true) 62: { 63: propertyCustomizer.Key(x => x.Column(member.LocalMember.DeclaringType.Name + "_Id")); 64: 65: Type sourceType = member.LocalMember.DeclaringType; 66: Type destinationType = member.LocalMember.GetPropertyOrFieldType().GetGenericArguments().First(); 67: IEnumerable<String> names = new Type[] { sourceType, destinationType }.Select(x => x.Name).OrderBy(x => x); 68: 69: //set inverse on the relation of the alphabetically first entity name 70: propertyCustomizer.Inverse(sourceType.Name == names.First()); 71: //set mapping table name from the entity names in alphabetical order 72: propertyCustomizer.Table(String.Join("_", names)); 73: } 74: } 75: } Conclusion Of course, there is much more to mapping than this, I suggest you look at all the events and functions offered by the ModelMapper to see where you can hook for making it behave the way you want. If you need any help, just let me know!

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StreamInsight 2.1, meet LINQ

- by Roman Schindlauer

Someone recently called LINQ “magic” in my hearing. I leapt to LINQ’s defense immediately. Turns out some people don’t realize “magic” is can be a pejorative term. I thought LINQ needed demystification. Here’s your best demystification resource: http://blogs.msdn.com/b/mattwar/archive/2008/11/18/linq-links.aspx. I won’t repeat much of what Matt Warren says in his excellent series, but will talk about some core ideas and how they affect the 2.1 release of StreamInsight. Let’s tell the story of a LINQ query. Compile time It begins with some code: IQueryable<Product> products = ...; var query = from p in products where p.Name == "Widget" select p.ProductID; foreach (int id in query) { ... When the code is compiled, the C# compiler (among other things) de-sugars the query expression (see C# spec section 7.16): ... var query = products.Where(p => p.Name == "Widget").Select(p => p.ProductID); ... Overload resolution subsequently binds the Queryable.Where<Product> and Queryable.Select<Product, int> extension methods (see C# spec sections 7.5 and 7.6.5). After overload resolution, the compiler knows something interesting about the anonymous functions (lambda syntax) in the de-sugared code: they must be converted to expression trees, i.e.,“an object structure that represents the structure of the anonymous function itself” (see C# spec section 6.5). The conversion is equivalent to the following rewrite: ... var prm1 = Expression.Parameter(typeof(Product), "p"); var prm2 = Expression.Parameter(typeof(Product), "p"); var query = Queryable.Select<Product, int>( Queryable.Where<Product>( products, Expression.Lambda<Func<Product, bool>>(Expression.Property(prm1, "Name"), prm1)), Expression.Lambda<Func<Product, int>>(Expression.Property(prm2, "ProductID"), prm2)); ... If the “products” expression had type IEnumerable<Product>, the compiler would have chosen the Enumerable.Where and Enumerable.Select extension methods instead, in which case the anonymous functions would have been converted to delegates. At this point, we’ve reduced the LINQ query to familiar code that will compile in C# 2.0. (Note that I’m using C# snippets to illustrate transformations that occur in the compiler, not to suggest a viable compiler design!) Runtime When the above program is executed, the Queryable.Where method is invoked. It takes two arguments. The first is an IQueryable<> instance that exposes an Expression property and a Provider property. The second is an expression tree. The Queryable.Where method implementation looks something like this: public static IQueryable<T> Where<T>(this IQueryable<T> source, Expression<Func<T, bool>> predicate) { return source.Provider.CreateQuery<T>( Expression.Call(this method, source.Expression, Expression.Quote(predicate))); } Notice that the method is really just composing a new expression tree that calls itself with arguments derived from the source and predicate arguments. Also notice that the query object returned from the method is associated with the same provider as the source query. By invoking operator methods, we’re constructing an expression tree that describes a query. Interestingly, the compiler and operator methods are colluding to construct a query expression tree. The important takeaway is that expression trees are built in one of two ways: (1) by the compiler when it sees an anonymous function that needs to be converted to an expression tree, and; (2) by a query operator method that constructs a new queryable object with an expression tree rooted in a call to the operator method (self-referential). Next we hit the foreach block. At this point, the power of LINQ queries becomes apparent. The provider is able to determine how the query expression tree is evaluated! The code that began our story was intentionally vague about the definition of the “products” collection. Maybe it is a queryable in-memory collection of products: var products = new[] { new Product { Name = "Widget", ProductID = 1 } }.AsQueryable(); The in-memory LINQ provider works by rewriting Queryable method calls to Enumerable method calls in the query expression tree. It then compiles the expression tree and evaluates it. It should be mentioned that the provider does not blindly rewrite all Queryable calls. It only rewrites a call when its arguments have been rewritten in a way that introduces a type mismatch, e.g. the first argument to Queryable.Where<Product> being rewritten as an expression of type IEnumerable<Product> from IQueryable<Product>. The type mismatch is triggered initially by a “leaf” expression like the one associated with the AsQueryable query: when the provider recognizes one of its own leaf expressions, it replaces the expression with the original IEnumerable<> constant expression. I like to think of this rewrite process as “type irritation” because the rewritten leaf expression is like a foreign body that triggers an immune response (further rewrites) in the tree. The technique ensures that only those portions of the expression tree constructed by a particular provider are rewritten by that provider: no type irritation, no rewrite. Let’s consider the behavior of an alternative LINQ provider. If “products” is a collection created by a LINQ to SQL provider: var products = new NorthwindDataContext().Products; the provider rewrites the expression tree as a SQL query that is then evaluated by your favorite RDBMS. The predicate may ultimately be evaluated using an index! In this example, the expression associated with the Products property is the “leaf” expression. StreamInsight 2.1 For the in-memory LINQ to Objects provider, a leaf is an in-memory collection. For LINQ to SQL, a leaf is a table or view. When defining a “process” in StreamInsight 2.1, what is a leaf? To StreamInsight a leaf is logic: an adapter, a sequence, or even a query targeting an entirely different LINQ provider! How do we represent the logic? Remember that a standing query may outlive the client that provisioned it. A reference to a sequence object in the client application is therefore not terribly useful. But if we instead represent the code constructing the sequence as an expression, we can host the sequence in the server: using (var server = Server.Connect(...)) { var app = server.Applications["my application"]; var source = app.DefineObservable(() => Observable.Range(0, 10, Scheduler.NewThread)); var query = from i in source where i % 2 == 0 select i; } Example 1: defining a source and composing a query Let’s look in more detail at what’s happening in example 1. We first connect to the remote server and retrieve an existing app. Next, we define a simple Reactive sequence using the Observable.Range method. Notice that the call to the Range method is in the body of an anonymous function. This is important because it means the source sequence definition is in the form of an expression, rather than simply an opaque reference to an IObservable<int> object. The variation in Example 2 fails. Although it looks similar, the sequence is now a reference to an in-memory observable collection: var local = Observable.Range(0, 10, Scheduler.NewThread); var source = app.DefineObservable(() => local); // can’t serialize ‘local’! Example 2: error referencing unserializable local object The Define* methods support definitions of operator tree leaves that target the StreamInsight server. These methods all have the same basic structure. The definition argument is a lambda expression taking between 0 and 16 arguments and returning a source or sink. The method returns a proxy for the source or sink that can then be used for the usual style of LINQ query composition. The “define” methods exploit the compile-time C# feature that converts anonymous functions into translatable expression trees! Query composition exploits the runtime pattern that allows expression trees to be constructed by operators taking queryable and expression (Expression<>) arguments. The practical upshot: once you’ve Defined a source, you can compose LINQ queries in the familiar way using query expressions and operator combinators. Notably, queries can be composed using pull-sequences (LINQ to Objects IQueryable<> inputs), push sequences (Reactive IQbservable<> inputs), and temporal sequences (StreamInsight IQStreamable<> inputs). You can even construct processes that span these three domains using “bridge” method overloads (ToEnumerable, ToObservable and To*Streamable). Finally, the targeted rewrite via type irritation pattern is used to ensure that StreamInsight computations can leverage other LINQ providers as well. Consider the following example (this example depends on Interactive Extensions): var source = app.DefineEnumerable((int id) => EnumerableEx.Using(() => new NorthwindDataContext(), context => from p in context.Products where p.ProductID == id select p.ProductName)); Within the definition, StreamInsight has no reason to suspect that it ‘owns’ the Queryable.Where and Queryable.Select calls, and it can therefore defer to LINQ to SQL! Let’s use this source in the context of a StreamInsight process: var sink = app.DefineObserver(() => Observer.Create<string>(Console.WriteLine)); var query = from name in source(1).ToObservable() where name == "Widget" select name; using (query.Bind(sink).Run("process")) { ... } When we run the binding, the source portion which filters on product ID and projects the product name is evaluated by SQL Server. Outside of the definition, responsibility for evaluation shifts to the StreamInsight server where we create a bridge to the Reactive Framework (using ToObservable) and evaluate an additional predicate. It’s incredibly easy to define computations that span multiple domains using these new features in StreamInsight 2.1! Regards, The StreamInsight Team

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ViewModel with SelectList binding in ASP.NET MVC2

- by Junto

I am trying to implement an Edit ViewModel for my Linq2SQL entity called Product. It has a foreign key linked to a list of brands. Currently I am populating the brand list via ViewData and using DropDownListFor, thus: <div class="editor-field"> <%= Html.DropDownListFor(model => model.BrandId, (SelectList)ViewData["Brands"])%> <%= Html.ValidationMessageFor(model => model.BrandId) %> </div> Now I want to refactor the view to use a strongly typed ViewModel and Html.EditorForModel(): <% using (Html.BeginForm()) {%> <%= Html.ValidationSummary(true) %> <fieldset> <legend>Fields</legend> <%=Html.EditorForModel() %> <p> <input type="submit" value="Save" /> </p> </fieldset> <% } %> In my Edit ViewModel, I have the following: public class EditProductViewModel { [HiddenInput] public int ProductId { get; set; } [Required()] [StringLength(200)] public string Name { get; set; } [Required()] [DataType(DataType.Html)] public string Description { get; set; } public IEnumerable<SelectListItem> Brands { get; set; } public int BrandId { get; set; } public EditProductViewModel(Product product, IEnumerable<SelectListItem> brands) { this.ProductId = product.ProductId; this.Name = product.Name; this.Description = product.Description; this.Brands = brands; this.BrandId = product.BrandId; } } The controller is setup like so: public ActionResult Edit(int id) { BrandRepository br = new BrandRepository(); Product p = _ProductRepository.Get(id); IEnumerable<SelectListItem> brands = br.GetAll().ToList().ToSelectListItems(p.BrandId); EditProductViewModel model = new EditProductViewModel(p, brands); return View("Edit", model); } The ProductId, Name and Description display correctly in the generated view, but the select list does not. The brand list definitely contains data. If I do the following in my view, the SelectList is visible: <% using (Html.BeginForm()) {%> <%= Html.ValidationSummary(true) %> <fieldset> <legend>Fields</legend> <%=Html.EditorForModel() %> <div class="editor-label"> <%= Html.LabelFor(model => model.BrandId) %> </div> <div class="editor-field"> <%= Html.DropDownListFor(model => model.BrandId, Model.Brands)%> <%= Html.ValidationMessageFor(model => model.BrandId) %> </div> <p> <input type="submit" value="Save" /> </p> </fieldset> <% } %> What am I doing wrong? Does EditorForModel() not generically support the SelectList? Am I missing some kind of DataAnnotation? I can't seem to find any examples of SelectList usage in ViewModels that help. I'm truly stumped. This answer seems to be close, but hasn't helped.

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building median for each string in IList<IDictionary<string, double>>

- by Oliver

Actually i have a little brain bender and and just can't find the right direction to get it to work: Given is an IList<IDictionary<string, double>> and it is filled as followed: Name|Value ----+----- "x" | 3.8 "y" | 4.2 "z" | 1.5 ----+----- "x" | 7.2 "y" | 2.9 "z" | 1.3 ----+----- ... | ... To fill this up with some random data i used the following methods: var list = CreateRandomPoints(new string[] { "x", "y", "z" }, 20); This will work as followed: private IList<IDictionary<string, double>> CreateRandomPoints(string[] variableNames, int count) { var list = new List<IDictionary<string, double>>(count); list.AddRange(CreateRandomPoints(variableNames).Take(count)); return list; } private IEnumerable<IDictionary<string, double>> CreateRandomPoints(string[] variableNames) { while (true) yield return CreateRandomLine(variableNames); } private IDictionary<string, double> CreateRandomLine(string[] variableNames) { var dict = new Dictionary<string, double>(variableNames.Length); foreach (var variable in variableNames) { dict.Add(variable, _Rand.NextDouble() * 10); } return dict; } Also i can say that it is already ensured that every Dictionary within the list contains the same keys (but from list to list the names and count of the keys can change). So that's what i got. Now to the things i need: I'd like to get the median (or any other math aggregate operation) of each Key within all the dictionaries, so that my function to call would look something like: IDictionary<string, double> GetMedianOfRows(this IList<IDictionary<string, double>> list) The best would be to give some kind of aggregate operation as a parameter to the function to make it more generic (don't know if the func has the correct parameters, but should imagine what i'd like to do): private IDictionary<string, double> Aggregate(this IList<IDictionary<string, double>> list, Func<IEnumerable<double>, double> aggregator) Also my actual biggest problem is to do the job with a single iteration over the list, cause if within the list are 20 variables with 1000 values i don't like to iterate 20 times over the list. Instead i would go one time over the list and compute all twenty variables at once (The biggest advantage of doing it that way would be to use this also as IEnumerable<T> on any part of the list in a later step). So here is the code i already got: public static IDictionary<string, double> GetMedianOfRows(this IList<IDictionary<string, double>> list) { //Check of parameters is left out! //Get first item for initialization of result dictionary var firstItem = list[0]; //Create result dictionary and fill in variable names var dict = new Dictionary<string, double>(firstItem.Count); //Iterate over the whole list foreach (IDictionary<string, double> row in list) { //Iterate over each key/value pair within the list foreach (var kvp in row) { //How to determine median of all values? } } return dict; } Just to be sure here is a little explanation about the Median.

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Generic Sorting using C# and Lambda Expression

- by Haitham Khedre

Download : GenericSortTester.zip I worked in this class from long time and I think it is a nice piece of code that I need to share , it might help other people searching for the same concept. this will help you to sort any collection easily without needing to write special code for each data type , however if you need special ordering you still can do it , leave a comment and I will see if I need to write another article to cover the other cases. I attached also a fully working example to make you able to see how do you will use that . public static class GenericSorter { public static IOrderedEnumerable<T> Sort<T>(IEnumerable<T> toSort, Dictionary<string, SortingOrder> sortOptions) { IOrderedEnumerable<T> orderedList = null; foreach (KeyValuePair<string, SortingOrder> entry in sortOptions) { if (orderedList != null) { if (entry.Value == SortingOrder.Ascending) { orderedList = orderedList.ApplyOrder<T>(entry.Key, "ThenBy"); } else { orderedList = orderedList.ApplyOrder<T>(entry.Key,"ThenByDescending"); } } else { if (entry.Value == SortingOrder.Ascending) { orderedList = toSort.ApplyOrder<T>(entry.Key, "OrderBy"); } else { orderedList = toSort.ApplyOrder<T>(entry.Key, "OrderByDescending"); } } } return orderedList; } private static IOrderedEnumerable<T> ApplyOrder<T> (this IEnumerable<T> source, string property, string methodName) { ParameterExpression param = Expression.Parameter(typeof(T), "x"); Expression expr = param; foreach (string prop in property.Split('.')) { expr = Expression.PropertyOrField(expr, prop); } Type delegateType = typeof(Func<,>).MakeGenericType(typeof(T), expr.Type); LambdaExpression lambda = Expression.Lambda(delegateType, expr, param); MethodInfo mi = typeof(Enumerable).GetMethods().Single( method => method.Name == methodName && method.IsGenericMethodDefinition && method.GetGenericArguments().Length == 2 && method.GetParameters().Length == 2) .MakeGenericMethod(typeof(T), expr.Type); return (IOrderedEnumerable<T>)mi.Invoke (null, new object[] { source, lambda.Compile() }); } } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }

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