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  • Entity Framework version 1- Brief Synopsis and Tips &ndash; Part 1

    - by Rohit Gupta
    To Do Eager loading use Projections (for e.g. from c in context.Contacts select c, c.Addresses)  or use Include Query Builder Methods (Include(“Addresses”)) If there is multi-level hierarchical Data then to eager load all the relationships use Include Query Builder methods like customers.Include("Order.OrderDetail") to include Order and OrderDetail collections or use customers.Include("Order.OrderDetail.Location") to include all Order, OrderDetail and location collections with a single include statement =========================================================================== If the query uses Joins then Include() Query Builder method will be ignored, use Nested Queries instead If the query does projections then Include() Query Builder method will be ignored Use Address.ContactReference.Load() OR Contact.Addresses.Load() if you need to Deferred Load Specific Entity – This will result in extra round trips to the database ObjectQuery<> cannot return anonymous types... it will return a ObjectQuery<DBDataRecord> Only Include method can be added to Linq Query Methods Any Linq Query method can be added to Query Builder methods. If you need to append a Query Builder Method (other than Include) after a LINQ method  then cast the IQueryable<Contact> to ObjectQuery<Contact> and then append the Query Builder method to it =========================================================================== Query Builder methods are Select, Where, Include Methods which use Entity SQL as parameters e.g. "it.StartDate, it.EndDate" When Query Builder methods do projection then they return ObjectQuery<DBDataRecord>, thus to iterate over this collection use contact.Item[“Name”].ToString() When Linq To Entities methods do projection, they return collection of anonymous types --- thus the collection is strongly typed and supports Intellisense EF Object Context can track changes only on Entities, not on Anonymous types. If you use a Defining Query for a EntitySet then the EntitySet becomes readonly since a Defining Query is the same as a View (which is treated as a ReadOnly by default). However if you want to use this EntitySet for insert/update/deletes then we need to map stored procs (as created in the DB) to the insert/update/delete functions of the Entity in the Designer You can use either Execute method or ToList() method to bind data to datasources/bindingsources If you use the Execute Method then remember that you can traverse through the ObjectResult<> collection (returned by Execute) only ONCE. In WPF use ObservableCollection to bind to data sources , for keeping track of changes and letting EF send updates to the DB automatically. Use Extension Methods to add logic to Entities. For e.g. create extension methods for the EntityObject class. Create a method in ObjectContext Partial class and pass the entity as a parameter, then call this method as desired from within each entity. ================================================================ DefiningQueries and Stored Procedures: For Custom Entities, one can use DefiningQuery or Stored Procedures. Thus the Custom Entity Collection will be populated using the DefiningQuery (of the EntitySet) or the Sproc. If you use Sproc to populate the EntityCollection then the query execution is immediate and this execution happens on the Server side and any filters applied will be applied in the Client App. If we use a DefiningQuery then these queries are composable, meaning the filters (if applied to the entityset) will all be sent together as a single query to the DB, returning only filtered results. If the sproc returns results that cannot be mapped to existing entity, then we first create the Entity/EntitySet in the CSDL using Designer, then create a dummy Entity/EntitySet using XML in the SSDL. When creating a EntitySet in the SSDL for this dummy entity, use a TSQL that does not return any results, but does return the relevant columns e.g. select ContactID, FirstName, LastName from dbo.Contact where 1=2 Also insure that the Entity created in the SSDL uses the SQL DataTypes and not .NET DataTypes. If you are unable to open the EDMX file in the designer then note the Errors ... they will give precise info on what is wrong. The Thrid option is to simply create a Native Query in the SSDL using <Function Name="PaymentsforContact" IsComposable="false">   <CommandText>SELECT ActivityId, Activity AS ActivityName, ImagePath, Category FROM dbo.Activities </CommandText></FuncTion> Then map this Function to a existing Entity. This is a quick way to get a custom Entity which is regular Entity with renamed columns or additional columns (which are computed columns). The disadvantage to using this is that It will return all the rows from the Defining query and any filter (if defined) will be applied only at the Client side (after getting all the rows from DB). If you you DefiningQuery instead then we can use that as a Composable Query. The Fourth option (for mapping a READ stored proc results to a non-existent Entity) is to create a View in the Database which returns all the fields that the sproc also returns, then update the Model so that the model contains this View as a Entity. Then map the Read Sproc to this View Entity. The other option would be to simply create the View and remove the sproc altogether. ================================================================ To Execute a SProc that does not return a entity, use a EntityCommand to execute that proc. You cannot call a sproc FunctionImport that does not return Entities From Code, the only way is to use SSDL function calls using EntityCommand.  This changes with EntityFramework Version 4 where you can return Scalar Types, Complex Types, Entities or NonQuery ================================================================ UDF when created as a Function in SSDL, we need to set the Name & IsComposable properties for the Function element. IsComposable is always false for Sprocs, for UDF's set this to true. You cannot call UDF "Function" from within code since you cannot import a UDF Function into the CSDL Model (with Version 1 of EF). only stored procedures can be imported and then mapped to a entity ================================================================ Entity Framework requires properties that are involved in association mappings to be mapped in all of the function mappings for the entity (Insert, Update and Delete). Because Payment has an association to Reservation... hence we need to pass both the paymentId and reservationId to the Delete sproc even though just the paymentId is the PK on the Payment Table. ================================================================ When mapping insert, update and delete procs to a Entity, insure that all the three or none are mapped. Further if you have a base class and derived class in the CSDL, then you must map (ins, upd, del) sprocs to all parent and child entities in the inheritance relationship. Note that this limitation that base and derived entity methods must all must be mapped does not apply when you are mapping Read Stored Procedures.... ================================================================ You can write stored procedures SQL directly into the SSDL by creating a Function element in the SSDL and then once created, you can map this Function to a CSDL Entity directly in the designer during Function Import ================================================================ You can do Entity Splitting such that One Entity maps to multiple tables in the DB. For e.g. the Customer Entity currently derives from Contact Entity...in addition it also references the ContactPersonalInfo Entity. One can copy all properties from the ContactPersonalInfo Entity into the Customer Entity and then Delete the CustomerPersonalInfo entity, finall one needs to map the copied properties to the ContactPersonalInfo Table in Table Mapping (by adding another table (ContactPersonalInfo) to the Table Mapping... this is called Entity Splitting. Thus now when you insert a Customer record, it will automatically create SQL to insert records into the Contact, Customers and ContactPersonalInfo tables even though you have a Single Entity called Customer in the CSDL =================================================================== There is Table by Type Inheritance where another EDM Entity can derive from another EDM entity and absorb the inherted entities properties, for example in the Break Away Geek Adventures EDM, the Customer entity derives (inherits) from the Contact Entity and absorbs all the properties of Contact entity. Thus when you create a Customer Entity in Code and then call context.SaveChanges the Object Context will first create the TSQL to insert into the Contact Table followed by a TSQL to insert into the Customer table =================================================================== Then there is the Table per Hierarchy Inheritance..... where different types are created based on a condition (similar applying a condition to filter a Entity to contain filtered records)... the diference being that the filter condition populates a new Entity Type (derived from the base Entity). In the BreakAway sample the example is Lodging Entity which is a Abstract Entity and Then Resort and NonResort Entities which derive from Lodging Entity and records are filtered based on the value of the Resort Boolean field =================================================================== Then there is Table per Concrete Type Hierarchy where we create a concrete Entity for each table in the database. In the BreakAway sample there is a entity for the Reservation table and another Entity for the OldReservation table even though both the table contain the same number of fields. The OldReservation Entity can then inherit from the Reservation Entity and configure the OldReservation Entity to remove all Scalar Properties from the Entity (since it inherits the properties from Reservation and filters based on ReservationDate field) =================================================================== Complex Types (Complex Properties) Entities in EF can also contain Complex Properties (in addition to Scalar Properties) and these Complex Properties reference a ComplexType (not a EntityType) DropdownList, ListBox, RadioButtonList, CheckboxList, Bulletedlist are examples of List server controls (not data bound controls) these controls cannot use Complex properties during databinding, they need Scalar Properties. So if a Entity contains Complex properties and you need to bind those to list server controls then use projections to return Scalar properties and bind them to the control (the disadvantage is that projected collections are not tracked by the Object Context and hence cannot persist changes to the projected collections bound to controls) ObjectDataSource and EntityDataSource do account for Complex properties and one can bind entities with Complex Properties to Data Source controls and they will be tracked for changes... with no additional plumbing needed to persist changes to these collections bound to controls So DataBound controls like GridView, FormView need to use EntityDataSource or ObjectDataSource as a datasource for entities that contain Complex properties so that changes to the datasource done using the GridView can be persisted to the DB (enabling the controls for updates)....if you cannot use the EntityDataSource you need to flatten the ComplexType Properties using projections With EF Version 4 ComplexTypes are supported by the Designer and can add/remove/compose Complex Types directly using the Designer =================================================================== Conditional Mapping ... is like Table per Hierarchy Inheritance where Entities inherit from a base class and then used conditions to populate the EntitySet (called conditional Mapping). Conditional Mapping has limitations since you can only use =, is null and IS NOT NULL Conditions to do conditional mapping. If you need more operators for filtering/mapping conditionally then use QueryView(or possibly Defining Query) to create a readonly entity. QueryView are readonly by default... the EntitySet created by the QueryView is enabled for change tracking by the ObjectContext, however the ObjectContext cannot create insert/update/delete TSQL statements for these Entities when SaveChanges is called since it is QueryView. One way to get around this limitation is to map stored procedures for the insert/update/delete operations in the Designer. =================================================================== Difference between QueryView and Defining Query : QueryView is defined in the (MSL) Mapping File/section of the EDM XML, whereas the DefiningQuery is defined in the store schema (SSDL). QueryView is written using Entity SQL and is this database agnostic and can be used against any database/Data Layer. DefiningQuery is written using Database Lanaguage i.e. TSQL or PSQL thus you have more control =================================================================== Performance: Lazy loading is deferred loading done automatically. lazy loading is supported with EF version4 and is on by default. If you need to turn it off then use context.ContextOptions.lazyLoadingEnabled = false To improve Performance consider PreCompiling the ObjectQuery using the CompiledQuery.Compile method

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  • Searching for entity awareness in 3D space algorithm and data structure

    - by Khanser
    I'm trying to do some huge AI system just for the fun and I've come to this problem. How can I let the AI entities know about each other without getting the CPU to perform redundant and costly work? Every entity has a spatial awareness zone and it has to know what's inside when it has to decide what to do. First thoughts, for every entity test if the other entities are inside the first's reach. Ok, so it was the first try and yep, that is redundant and costly. We are working with real time AI over 10000+ entities so this is not a solution. Second try, calculate some grid over the awareness zone of every entity and test whether in this zones are entities (we are working with 3D entities with float x,y,z location coordinates) testing every point in the grid with the indexed-by-coordinate entities. Well, I don't like this because is also costly, but not as the first one. Third, create some multi linked lists over the x's and y's indexed positions of the entities so when we search for an interval between x,y and z,w positions (this interval defines the square over the spatial awareness zone) over the multi linked list, we won't have 'voids'. This has the problem of finding the nearest proximity value if there isn't one at the position where we start the search. I'm not convinced with any of the ideas so I'm searching for some enlightening. Do you people have any better ideas?

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  • Expression Tree

    - by nettguy
    My understanding of expression tree is : Expression trees are in-memory representation of expression like arithmetic or boolean expression.The expressions are stored into the parsed tree.so we can easily transalate into any other language. Linq to SQL uses expression tree.Normally in LINQ to SQL query the compiler translates it into parsed expression trees.These are passed to Sql Server as T-SQL Statements.The Sql server executes the T-SQL query and sends down the result back.That is why when you execute LINQ to SQL you gets IQueryable<T> not IEnumetrable<T>.Because IQuerybale contains public IQueryable:IEnumerable { Type Element {get;} Expression Expression {get;} IQueryaleProvider Provider {get;} } Questions : Microsoft uses Expression trees to play with LINQ-to-Sql.What are the different ways can i use expression trees to boost my code. Apart from LINQ to SQL,Linq to amazon ,who used expression trees in their applications? Linq to Object return IEnumerable,Linq to SQL return IQueryable ,What does LINQ to XML return?

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  • Expression Tree : C#

    - by nettguy
    My understanding of expression tree is : Expression trees are in-memory representation of expression like arithmetic or boolean expression.The expressions are stored into the parsed tree.so we can easily transalate into any other language. Linq to SQL uses expression tree.Normally when our LINQ to SQL query compiler translates it to parsed expression trees.These are passed to Sql Server as T-SQL Statements.The Sql server executes the T-SQL query and sends down the result back.That is why when you execute LINQ to SQL you gets IQueryable<T> not IEnumetrable<T>.Because IQuerybale contains public IQueryable:IEnumerable { Type Element {get;} Expression Expression {get;} IQueryaleProvider Provider {get;} } Questions : Microsoft uses Expression trees to play with LINQ-to-Sql.What are the different ways can i use expression trees to boost my code. Apart from LINQ to SQL,Linq to amazon ,who used expression trees in their applications? Linq to Object return IEnumerable,Linq to SQL return IQueryable ,What does LINQ to XML return?

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  • Query.fetch(limit=2000) only moves cursor forward by 1000 entities?

    - by Liron
    Let's say I have 2500 MyModel entities in my datastore, and I run this code: query = MyModel.all() first_batch = query.fetch(2000) len(first_batch) # 2000 next_query = MyModel.all().with_cursor(query.cursor()) next_batch = next_query.fetch(2000) What do you think len(next_batch) is? 500, right? Nope - it's 1500. Apparently the query cursor never moves forward by more than 1000, even when the query itself returns more than 1000 entities. Should I do something different or is it just an App Engine bug?

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  • What is a good algorithm to distribute items with specific requirements?

    - by user66160
    I have to programmatically distribute a set of items to some entities, but there are rules both on the items and on the entities like so: Item one: 100 units, only entities from Foo Item two: 200 units, no restrictions Item three: 100 units, only entities that have Bar Entity one: Only items that have Baz Entity one hundred: No items that have Fubar I only need to be pointed in the right direction, I'll research and learn the suggested methods.

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  • How can I import the System.Linq namespace to Boo?

    - by OmiD Rezaei
    When I try to import the System.Linq namespace to Boo compiler, I get this error: Boo.Lang.Compiler.CompilerError: Namespace 'System.Linq' not found, maybe you forgot to add an assembly reference? I use "Rhino.DSL.dll" and my DSL engine code is here: public class MyDslEngine : DslEngine { protected override void CustomizeCompiler(BooCompiler compiler, CompilerPipeline pipeline, string[] urls) { pipeline.Insert(1, new AnonymousBaseClassCompilerStep(typeof(DslBase), "Prepare", "System.Linq", "Azarakhsh.Framework.Repository" //it's my repository framework )); pipeline.Insert(2, new UseSymbolsStep()); pipeline.Insert(3, new RunScriptCompilerStep()); } }

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  • Retrieve data from an ASP.Net application using ADO.Net 2.0 connected model

    - by nikolaosk
    I have been teaching Entity Framework,LINQ to SQL,LINQ to objects,LINQ to XML for some time now. I am huge fan of LINQ to Entities and I am using Entity Framework as my main data access technology. Entity framework is in the second version right now and I can accomplish most of the things I need. I am sure the guys in the ADO.Net team will implement many more features in the future. I am a strong believer that you cannot really understand the benefits of LINQ to SQL or LINQ to Entities unless you...(read more)

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  • Faster, Simpler access to Azure Tables with Enzo Azure API

    - by Herve Roggero
    After developing the latest version of Enzo Cloud Backup I took the time to create an API that would simplify access to Azure Tables (the Enzo Azure API). At first, my goal was to make the code simpler compared to the Microsoft Azure SDK. But as it turns out it is also a little faster; and when using the specialized methods (the fetch strategies) it is much faster out of the box than the Microsoft SDK, unless you start creating complex parallel and resilient routines yourself. Last but not least, I decided to add a few extension methods that I think you will find attractive, such as the ability to transform a list of entities into a DataTable. So let’s review each area in more details. Simpler Code My first objective was to make the API much easier to use than the Azure SDK. I wanted to reduce the amount of code necessary to fetch entities, remove the code needed to add automatic retries and handle transient conditions, and give additional control, such as a way to cancel operations, obtain basic statistics on the calls, and control the maximum number of REST calls the API generates in an attempt to avoid throttling conditions in the first place (something you cannot do with the Azure SDK at this time). Strongly Typed Before diving into the code, the following examples rely on a strongly typed class called MyData. The way MyData is defined for the Azure SDK is similar to the Enzo Azure API, with the exception that they inherit from different classes. With the Azure SDK, classes that represent entities must inherit from TableServiceEntity, while classes with the Enzo Azure API must inherit from BaseAzureTable or implement a specific interface. // With the SDK public class MyData1 : TableServiceEntity {     public string Message { get; set; }     public string Level { get; set; }     public string Severity { get; set; } } //  With the Enzo Azure API public class MyData2 : BaseAzureTable {     public string Message { get; set; }     public string Level { get; set; }     public string Severity { get; set; } } Simpler Code Now that the classes representing an Azure Table entity are defined, let’s review the methods that the Azure SDK would look like when fetching all the entities from an Azure Table (note the use of a few variables: the _tableName variable stores the name of the Azure Table, and the ConnectionString property returns the connection string for the Storage Account containing the table): // With the Azure SDK public List<MyData1> FetchAllEntities() {      CloudStorageAccount storageAccount = CloudStorageAccount.Parse(ConnectionString);      CloudTableClient tableClient = storageAccount.CreateCloudTableClient();      TableServiceContext serviceContext = tableClient.GetDataServiceContext();      CloudTableQuery<MyData1> partitionQuery =         (from e in serviceContext.CreateQuery<MyData1>(_tableName)         select new MyData1()         {            PartitionKey = e.PartitionKey,            RowKey = e.RowKey,            Timestamp = e.Timestamp,            Message = e.Message,            Level = e.Level,            Severity = e.Severity            }).AsTableServiceQuery<MyData1>();        return partitionQuery.ToList();  } This code gives you automatic retries because the AsTableServiceQuery does that for you. Also, note that this method is strongly-typed because it is using LINQ. Although this doesn’t look like too much code at first glance, you are actually mapping the strongly-typed object manually. So for larger entities, with dozens of properties, your code will grow. And from a maintenance standpoint, when a new property is added, you may need to change the mapping code. You will also note that the mapping being performed is optional; it is desired when you want to retrieve specific properties of the entities (not all) to reduce the network traffic. If you do not specify the properties you want, all the properties will be returned; in this example we are returning the Message, Level and Severity properties (in addition to the required PartitionKey, RowKey and Timestamp). The Enzo Azure API does the mapping automatically and also handles automatic reties when fetching entities. The equivalent code to fetch all the entities (with the same three properties) from the same Azure Table looks like this: // With the Enzo Azure API public List<MyData2> FetchAllEntities() {        AzureTable at = new AzureTable(_accountName, _accountKey, _ssl, _tableName);        List<MyData2> res = at.Fetch<MyData2>("", "Message,Level,Severity");        return res; } As you can see, the Enzo Azure API returns the entities already strongly typed, so there is no need to map the output. Also, the Enzo Azure API makes it easy to specify the list of properties to return, and to specify a filter as well (no filter was provided in this example; the filter is passed as the first parameter).  Fetch Strategies Both approaches discussed above fetch the data sequentially. In addition to the linear/sequential fetch methods, the Enzo Azure API provides specific fetch strategies. Fetch strategies are designed to prepare a set of REST calls, executed in parallel, in a way that performs faster that if you were to fetch the data sequentially. For example, if the PartitionKey is a GUID string, you could prepare multiple calls, providing appropriate filters ([‘a’, ‘b’[, [‘b’, ‘c’[, [‘c’, ‘d[, …), and send those calls in parallel. As you can imagine, the code necessary to create these requests would be fairly large. With the Enzo Azure API, two strategies are provided out of the box: the GUID and List strategies. If you are interested in how these strategies work, see the Enzo Azure API Online Help. Here is an example code that performs parallel requests using the GUID strategy (which executes more than 2 t o3 times faster than the sequential methods discussed previously): public List<MyData2> FetchAllEntitiesGUID() {     AzureTable at = new AzureTable(_accountName, _accountKey, _ssl, _tableName);     List<MyData2> res = at.FetchWithGuid<MyData2>("", "Message,Level,Severity");     return res; } Faster Results With Sequential Fetch Methods Developing a faster API wasn’t a primary objective; but it appears that the performance tests performed with the Enzo Azure API deliver the data a little faster out of the box (5%-10% on average, and sometimes to up 50% faster) with the sequential fetch methods. Although the amount of data is the same regardless of the approach (and the REST calls are almost exactly identical), the object mapping approach is different. So it is likely that the slight performance increase is due to a lighter API. Using LINQ offers many advantages and tremendous flexibility; nevertheless when fetching data it seems that the Enzo Azure API delivers faster.  For example, the same code previously discussed delivered the following results when fetching 3,000 entities (about 1KB each). The average elapsed time shows that the Azure SDK returned the 3000 entities in about 5.9 seconds on average, while the Enzo Azure API took 4.2 seconds on average (39% improvement). With Fetch Strategies When using the fetch strategies we are no longer comparing apples to apples; the Azure SDK is not designed to implement fetch strategies out of the box, so you would need to code the strategies yourself. Nevertheless I wanted to provide out of the box capabilities, and as a result you see a test that returned about 10,000 entities (1KB each entity), and an average execution time over 5 runs. The Azure SDK implemented a sequential fetch while the Enzo Azure API implemented the List fetch strategy. The fetch strategy was 2.3 times faster. Note that the following test hit a limit on my network bandwidth quickly (3.56Mbps), so the results of the fetch strategy is significantly below what it could be with a higher bandwidth. Additional Methods The API wouldn’t be complete without support for a few important methods other than the fetch methods discussed previously. The Enzo Azure API offers these additional capabilities: - Support for batch updates, deletes and inserts - Conversion of entities to DataRow, and List<> to a DataTable - Extension methods for Delete, Merge, Update, Insert - Support for asynchronous calls and cancellation - Support for fetch statistics (total bytes, total REST calls, retries…) For more information, visit http://www.bluesyntax.net or go directly to the Enzo Azure API page (http://www.bluesyntax.net/EnzoAzureAPI.aspx). About Herve Roggero Herve Roggero, Windows Azure MVP, is the founder of Blue Syntax Consulting, a company specialized in cloud computing products and services. Herve's experience includes software development, architecture, database administration and senior management with both global corporations and startup companies. Herve holds multiple certifications, including an MCDBA, MCSE, MCSD. He also holds a Master's degree in Business Administration from Indiana University. Herve is the co-author of "PRO SQL Azure" from Apress and runs the Azure Florida Association (on LinkedIn: http://www.linkedin.com/groups?gid=4177626). For more information on Blue Syntax Consulting, visit www.bluesyntax.net.

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  • A question about entities, roles and interfaces in Entity Framework 4.

    - by mvole
    Hi, I am an experienced .NET developer but new to EF - so please bear with me. I will use an example of a college application to illustrate my problem. I have these user roles: Lecturer, Student, Administrator. In my code I envisage working with these entities as distinct classes so e.g. a Lecturer teaches a collection of Students. And work with 'is Student' 'TypeOf' etc. Each of these entities share lots of common properties/methods e.g. they can all log onto the system and do stuff related to their role. In EF designer I can create a base entity Person (or User...) and have Lecturer, Student and Administrator all inherit from that. The difficulty I have is that a Lecturer can be an Administrator - and in fact on occasion a Student can be a Lecturer. If I were to add other entities such as Employee and Warden then this gets even more of an issue. I could presumably work with Interfaces so a person could implement ILecturer and IStudent, however I do not see how this fits within EF. I would like to work within the EF designer if possible and I'm working model-first (coding in C#). So any help and advice/samples would be very welcome and much appreciated. Thanks

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  • Distinctly LINQ &ndash; Getting a Distinct List of Objects

    - by David Totzke
    Let’s say that you have a list of objects that contains duplicate items and you want to extract a subset of distinct items.  This is pretty straight forward in the trivial case where the duplicate objects are considered the same such as in the following example: List<int> ages = new List<int> { 21, 46, 46, 55, 17, 21, 55, 55 }; IEnumerable<int> distinctAges = ages.Distinct(); Console.WriteLine("Distinct ages:"); foreach (int age in distinctAges) { Console.WriteLine(age); } /* This code produces the following output: Distinct ages: 21 46 55 17 */ What if you are working with reference types instead?  Imagine a list of search results where items in the results, while unique in and of themselves, also point to a parent.  We’d like to be able to select a bunch of items in the list but then see only a distinct list of parents.  Distinct isn’t going to help us much on its own as all of the items are distinct already.  Perhaps we can create a class with just the information we are interested in like the Id and Name of the parents.  public class SelectedItem { public int ItemID { get; set; } public string DisplayName { get; set; } } We can then use LINQ to populate a list containing objects with just the information we are interested in and then get rid of the duplicates. IEnumerable<SelectedItem> list = (from item in ResultView.SelectedRows.OfType<Contract.ReceiptSelectResults>() select new SelectedItem { ItemID = item.ParentId, DisplayName = item.ParentName }) .Distinct(); Most of you will have guessed that this didn’t work.  Even though some of our objects are now duplicates, because we are working with reference types, it doesn’t matter that their properties are the same, they’re still considered unique.  What we need is a way to define equality for the Distinct() extension method. IEqualityComparer<T> Looking at the Distinct method we see that there is an overload that accepts an IEqualityComparer<T>.  We can simply create a class that implements this interface and that allows us to define equality for our SelectedItem class. public class SelectedItemComparer : IEqualityComparer<SelectedItem> { public new bool Equals(SelectedItem abc, SelectedItem def) { return abc.ItemID == def.ItemID && abc.DisplayName == def.DisplayName; } public int GetHashCode(SelectedItem obj) { string code = obj.DisplayName + obj.ItemID.ToString(); return code.GetHashCode(); } } In the Equals method we simply do whatever comparisons are necessary to determine equality and then return true or false.  Take note of the implementation of the GetHashCode method.  GetHashCode must return the same value for two different objects if our Equals method says they are equal.  Get this wrong and your comparer won’t work .  Even though the Equals method returns true, mismatched hash codes will cause the comparison to fail.  For our example, we simply build a string from the properties of the object and then call GetHashCode() on that. Now all we have to do is pass an instance of our IEqualitlyComarer<T> to Distinct and all will be well: IEnumerable<SelectedItem> list =     (from item in ResultView.SelectedRows.OfType<Contract.ReceiptSelectResults>()         select new SelectedItem { ItemID = item.dahfkp, DisplayName = item.document_code })                         .Distinct(new SelectedItemComparer());   Enjoy. Dave Just because I can… Technorati Tags: LINQ,C#

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  • When following SRP, how should I deal with validating and saving entities?

    - by Kristof Claes
    I've been reading Clean Code and various online articles about SOLID lately, and the more I read about it, the more I feel like I don't know anything. Let's say I'm building a web application using ASP.NET MVC 3. Let's say I have a UsersController with a Create action like this: public class UsersController : Controller { public ActionResult Create(CreateUserViewModel viewModel) { } } In that action method I want to save a user to the database if the data that was entered is valid. Now, according to the Single Responsibility Principle an object should have a single responsibility, and that responsibility should be entirely encapsulated by the class. All its services should be narrowly aligned with that responsibility. Since validation and saving to the database are two separate responsibilities, I guess I should create to separate class to handle them like this: public class UsersController : Controller { private ICreateUserValidator validator; private IUserService service; public UsersController(ICreateUserValidator validator, IUserService service) { this.validator = validator; this.service= service; } public ActionResult Create(CreateUserViewModel viewModel) { ValidationResult result = validator.IsValid(viewModel); if (result.IsValid) { service.CreateUser(viewModel); return RedirectToAction("Index"); } else { foreach (var errorMessage in result.ErrorMessages) { ModelState.AddModelError(String.Empty, errorMessage); } return View(viewModel); } } } That makes some sense to me, but I'm not at all sure that this is the right way to handle things like this. It is for example entirely possible to pass an invalid instance of CreateUserViewModel to the IUserService class. I know I could use the built in DataAnnotations, but what when they aren't enough? Image that my ICreateUserValidator checks the database to see if there already is another user with the same name... Another option is to let the IUserService take care of the validation like this: public class UserService : IUserService { private ICreateUserValidator validator; public UserService(ICreateUserValidator validator) { this.validator = validator; } public ValidationResult CreateUser(CreateUserViewModel viewModel) { var result = validator.IsValid(viewModel); if (result.IsValid) { // Save the user } return result; } } But I feel I'm violating the Single Responsibility Principle here. How should I deal with something like this?

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  • How to get scripted programs governing game entities run in parallel with a game loop?

    - by Jim
    I recently discovered Crobot which is (briefly) a game where each player codes a virtual robot in a pseudo-C language. Each robot is then put in an arena where it fights against other robots. A robots' source code has this shape : /* Beginning file robot.r */ main() { while (1) { /* Do whatever you want */ ... move(); ... fire(); } } /* End file robot.r */ You can see that : The code is totally independent from any library/include Some predefined functions are available (move, fire, etc…) The program has its own game loop, and consequently is not called every frame My question is: How to achieve a similar result using scripted languages in collaboration with a C/C++ main program ? I found a possible approach using Python, multi-threading and shared memory, although I am not sure yet that it is possible this way. TCP/IP seems a bit too complicated for this kind of application.

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  • How can I efficiently update only the entities that matter in a given frame?

    - by lezebulon
    I'm making a RTS, which can potentially have lots of units in one map (think Age of Empires). I'm looking for a way to update my units. I want to avoid calling a virtual Update() method every frame on every entity. On the other hand, units that are not in view should still be updated and behave "normally." I'm assuming this is a fairly standard question; what would be a way to handle this situation?

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  • Highlighting new rows in ADF Table

    - by Sireesha Pinninti
    About This article explains how to hightlight newly inserted rows in an ADF Table without writing any extra java/javascript code.IntroductionSometimes we may wish to give more clarification to the end user by differentiating between newly inserted rows and the existing rows(i.e the rows from DB) in a table by highlighting new rows in different color as in the figure shown below. SolutionWe can achieve the same by giving following EL to inlineStyle property of every column inside af:table: #{row.row.entities[0].entityState == 0?'background-color:#307D7E;':''}ExplanationHere is the explanation for row.row.entities[0].entityState given inside EL which returns the state of the row(i.e, New, Modified, Unmodified, Initialized etc.)row - Refers to a tree node binding(instance of FacesCtrlHierNodeBinding) at runtimerow.row - Refers to an instance of row that the tree node is based onrow.row.entities[0] - Gets the Entity row at zeroth index. In most of the cases, the table will be based on single entity. If your table is based on multiple entities then the index needs to be given accordingly.row.row.entities[0].entityState - Gets Entity Object's current Entity-state in the transaction.(0 - New, Modified - 2, Unmodified - 1, Initialized - -1,  etc.,)

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  • Is using HTML entities (for language-specific characters) in UTF-8 necessary?

    - by Drachenzauberei
    As in the subject-line. Saw the situation the other day on a page which felt weird to me. Except for markup-delimiting characters such as pointy brackets or the ampersand, escaping, say, German umlauts shouldn't be necessary, should it? Checked the encoding server-side, in-page and by way of HTTP headers, looks completely UTF-8 to me. What's your take on this and do you reckon it could adversely affect SEO or SERP placement?the page

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  • Entity Framework 4 POCO entities in separate assembly, Dynamic Data Website?

    - by steve.macdonald
    Basically I want to use a dynamic data website to maintain data in an EF4 model where the entities are in their own assembly. Model and context are in another assembly. I tried this http://stackoverflow.com/questions/2282916/entity-framework-4-self-tracking-entities-asp-net-dynamic-data-error but get an "ambiguous match" error from reflection: System.Reflection.AmbiguousMatchException was unhandled by user code Message=Ambiguous match found. Source=mscorlib StackTrace: at System.RuntimeType.GetPropertyImpl(String name, BindingFlags bindingAttr, Binder binder, Type returnType, Type[] types, ParameterModifier[] modifiers) at System.Type.GetProperty(String name) at System.Web.DynamicData.ModelProviders.EFTableProvider..ctor(EFDataModelProvider dataModel, EntitySet entitySet, EntityType entityType, Type entityClrType, Type parentEntityClrType, Type rootEntityClrType, String name) at System.Web.DynamicData.ModelProviders.EFDataModelProvider.CreateTableProvider(EntitySet entitySet, EntityType entityType) at System.Web.DynamicData.ModelProviders.EFDataModelProvider..ctor(Object contextInstance, Func1 contextFactory) at System.Web.DynamicData.ModelProviders.SchemaCreator.CreateDataModel(Object contextInstance, Func1 contextFactory) at System.Web.DynamicData.MetaModel.RegisterContext(Func`1 contextFactory, ContextConfiguration configuration) at WebApplication1.Global.RegisterRoutes(RouteCollection routes) in C:\dev\Puffin\Puffin.Prototype.Web\Global.asax.cs:line 42 at WebApplication1.Global.Application_Start(Object sender, EventArgs e) in C:\dev\Puffin\Puffin.Prototype.Web\Global.asax.cs:line 78 InnerException:

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  • Ninject 2 for CF3.5 TargetInvocationException

    - by jack london
    In middle of application when calling following line: var component = _Kernel.Get<IComponent>(); I'm getting TargetInvocationException. IComponent is a Form. at System.Reflection.RuntimeConstructorInfo.Invoke(BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture) at System.Reflection.ConstructorInfo.Invoke(Object[] parameters) at Ninject.Injection.ReflectionInjectorFactory.<c_DisplayClass1.b_0(Object[] args) at Ninject.Activation.Providers.StandardProvider.Create(IContext context) at Ninject.Activation.Context.Resolve() at Ninject.KernelBase.b_7(IContext context) at System.Linq.Enumerable.d_d2.MoveNext() at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable1 source) at Ninject.Planning.Targets.Target1.ResolveWithin(IContext parent) at Ninject.Activation.Providers.StandardProvider.GetValue(IContext context, ITarget target) at Ninject.Activation.Providers.StandardProvider.<>c__DisplayClass2.<Create>b__1(ITarget target) at System.Linq.Enumerable.<SelectIterator>d__d2.MoveNext() at System.Linq.Buffer1..ctor(IEnumerable1 source) at System.Linq.Enumerable.ToArray[TSource](IEnumerable1 source) at Ninject.Activation.Providers.StandardProvider.Create(IContext context) at Ninject.Activation.Context.Resolve() at Ninject.KernelBase.<Resolve>b__7(IContext context) at System.Linq.Enumerable.<SelectIterator>d__d2.MoveNext() at System.Linq.Enumerable.d__b01.MoveNext() at System.Linq.Enumerable.Single[TSource](IEnumerable1 source) at Ninject.ResolutionExtensions.Get[T](IResolutionRoot root, IParameter[] parameters)

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  • How to represent different entities that have identical behavior?

    - by Dominik
    I have several different entities in my domain model (animal species, let's say), which have a few properties each. The entities are readonly (they do not change state during the application lifetime) and they have identical behavior (the differ only by the values of properties). How to implement such entities in code? Unsuccessful attempts: Enums I tried an enum like this: enum Animals { Frog, Duck, Otter, Fish } And other pieces of code would switch on the enum. However, this leads to ugly switching code, scattering the logic around and problems with comboboxes. There's no pretty way to list all possible Animals. Serialization works great though. Subclasses I also thought about where each animal type is a subclass of a common base abstract class. The implementation of Swim() is the same for all Animals, though, so it makes little sense and serializability is a big issue now. Since we represent an animal type (species, if you will), there should be one instance of the subclass per application, which is hard and weird to maintain when we use serialization. public abstract class AnimalBase { string Name { get; set; } // user-readable double Weight { get; set; } Habitat Habitat { get; set; } public void Swim(); { /* swim implementation; the same for all animals but depends uses the value of Weight */ } } public class Otter: AnimalBase{ public Otter() { Name = "Otter"; Weight = 10; Habitat = "North America"; } } // ... and so on Just plain awful. Static fields This blog post gave me and idea for a solution where each option is a statically defined field inside the type, like this: public class Animal { public static readonly Animal Otter = new Animal { Name="Otter", Weight = 10, Habitat = "North America"} // the rest of the animals... public string Name { get; set; } // user-readable public double Weight { get; set; } public Habitat Habitat { get; set; } public void Swim(); } That would be great: you can use it like enums (AnimalType = Animal.Otter), you can easily add a static list of all defined animals, you have a sensible place where to implement Swim(). Immutability can be achieved by making property setters protected. There is a major problem, though: it breaks serializability. A serialized Animal would have to save all its properties and upon deserialization it would create a new instance of Animal, which is something I'd like to avoid. Is there an easy way to make the third attempt work? Any more suggestions for implementing such a model?

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  • Indexing SET field

    - by Dienow
    I have two entities A and B. They are related with many to many relation. Entity A can be related up to 100 B entities. Entity B can be related up to 10000 A entities. I need quick way to select for example 30 A entities, that have relation with specified B entities, filtered and sorted by different attributes. Here how I see ideal solution: I put all information I know about A entities, including their relations with B entities into single row (Special table with SET field) then add all necessary indexes. The problem is that you can't use index while querying by SET field. What should I do? I can replace database with something different, if that'll help.

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  • Why can't I retrieve the entities I've just persisted?

    - by felipecao
    I've got this web service that basically queries the database and returns all persisted entities. For testing purposes, I've created a TestDataManager that persists 2 example entities after Spring context is loaded (BTW, I'm using JAX-WS, Spring, Hibernate and HSQLDB). My TestDataManager looks like this: @Component public class TestDataManager { @Resource private SessionFactory sf; @PostConstruct @Transactional(readOnly = false, propagation = Propagation.REQUIRES_NEW) public void insertTestData(){ sf.openSession(); sf.openSession().beginTransaction(); sf.openSession().persist(new Site("site one")); sf.openSession().persist(new Site("site two")); sf.openSession().flush(); } } My JAX-WS endpoint looks like this: @WebService public class SmartBrickEndpoint { @Resource private WebServiceContext context; public Set<Site> getSitesForUser(String user){ return getSiteService().findByUser(new User(user)); } private ISiteService getSiteService(){ ServletContext servletContext = (ServletContext) context.getMessageContext().get("javax.xml.ws.servlet.context"); return (ISiteService) BeanRetriever.getBean(servletContext, ISiteService.class); } } This my Service class: @Component @Transactional(readOnly = true) public class SiteService implements ISiteService { @Resource private ISiteDao siteDao; @Override public Set<Site> findByUser(User user) { return siteDao.findByUser(user); } } This is my DAO: @Component @Transactional(readOnly = true) public class SiteDao implements ISiteDao { @Resource private SessionFactory sessionFactory; @Override public Set<Site> findByUser(User user) { Set<Site> sites = new LinkedHashSet<Site>(sessionFactory.getCurrentSession().createCriteria(Site.class).list()); return sites; } } This is my applicationContext.xml: <context:annotation-config /> <context:component-scan base-package="br.unirio.wsimxp.dao"/> <context:component-scan base-package="br.unirio.wsimxp.service"/> <context:component-scan base-package="br.unirio.wsimxp.spring"/> <bean id="applicationDS" class="org.springframework.jdbc.datasource.DriverManagerDataSource"> <property name="driverClassName" value="org.hsqldb.jdbcDriver"/> <property name="url" value="jdbc:hsqldb:file:sites"/> </bean> <bean id="sessionFactory" class="org.springframework.orm.hibernate3.annotation.AnnotationSessionFactoryBean"> <property name="dataSource" ref="applicationDS" /> <property name="configLocation"> <value>classpath:hibernate.cfg.xml</value> </property> <property name="hibernateProperties"> <props> <prop key="hibernate.dialect">org.hibernate.dialect.HSQLDialect</prop> <prop key="hibernate.show_sql">true</prop> <prop key="hibernate.format_sql">true</prop> <prop key="hibernate.connection.release_mode">on_close</prop> <!--<prop key="hibernate.current_session_context_class">thread</prop>--> <prop key="hibernate.query.factory_class">org.hibernate.hql.classic.ClassicQueryTranslatorFactory</prop> <prop key="hibernate.hbm2ddl.auto">create-drop</prop> </props> </property> </bean> <bean id="transactionManager" class="org.springframework.orm.hibernate3.HibernateTransactionManager"> <property name="sessionFactory" ref="sessionFactory" /> </bean> <tx:annotation-driven transaction-manager="transactionManager" /> This is what's going on now: when the app is deployed, TestDataManager#insertTestData kicks-in (due to @PostConstruct) and persist does not raise any exception. I should have 2 entities in the DB by now. Afterwards, I invoke the endpoint by a SOAP client, and the request goes all the way up to the DAO. The Hibernate invocation does not raise any exception, but the returned list is empty. The odd thing is, in TestDataManager, if I switch from sf.openSession() to sf.getCurrentSession(), I get an error message: "No Hibernate Session bound to thread, and configuration does not allow creation of non-transactional one here". What I am doing wrong here? Why is the query "not seeing" the persisted entities? Why do I need to invoke sf.openSession() on TestDataManager although it's annotated with @Transactional? I have done some tests with hibernate.current_session_context_class=thread in application.xml, but then I just switch problems in each class. I'd like not needing to manually invoke sf.openSession() and leave that for Hibernate to take care. Thanks a lot for any help!

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