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• Client-side Replication for SQL Server?

  - by Mighty Z

  I'd like to have some degree of fault tolerance / redundancy with my SQL Server Express database. I know that if I upgrade to a pricier version of SQL Server, I can get "Replication" built in. But I'm wondering if anyone has experience in managing replication on the client side. As in, from my application: Every time I need to create, update or delete records from the database -- issue the statement to all n servers directly from the client side Every time I need to read, I can do so from one representative server (other schemes seem possible here, too). It seems like this logic could potentially be added directly to my Linq-To-SQL Data Context. Any thoughts?

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• How the return type is determined in a method that uses Linq2Sql?

  - by Richard77

  Hello, I've usually have difficulties with return types when it comes to linq. I'll explain by the following examples. Let's say I have a Table Products with ProductID, Name, Category, and Price as columns : 1) IQueryable<Product public IQueryable<Product> GetChildrenProducts() { return (from pd in db.Products where pd.Category == "Children" select pd); } 2) Product public Product GetProduct(int id) { return (from pd in db.Products where pd.ProductID == id select pd).FirstOrDefault(); } Now, if I decide to select, for instance, only one column (Price or Name) or even 2 or 3 columns (Name and Price), but in any case, less than the 4 columns, what's going to be the return type? I mean this: public returnType GetSomeInformation() { return (from pd in db.Products select new { pd.Name, pd.Price } } What SHOULD BE the returnType for the GetSomeInformation()? Thanks for helping

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• How do I write this as an expression?

  - by itchi

  I'm trying to rewrite a linq to entities query to an expression. My model is a School can have many Persons where Persons are inherited out to teachers, students, etc. The following query works for me: IQueryable<DAL.TEACHER> teacher = from p in School select p.PERSON as ESBDAL.TEACHER; How would I write this as a query expression? I thought something like: IQueryable<DAL.TEACHER> teacher = School.Select(x=>x.PERSON) as IQueryable<DAL.TEACHER>; ...but it does not. Am I misunderstanding the .Select()?

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• Using Linq2Sql to insert data into multiple tables using an auto incremented primary key

  - by Thomas

  I have a Customer table with a Primary key (int auto increment) and an Address table with a foreign key to the Customer table. I am trying to insert both rows into the database in one nice transaction. using (DatabaseDataContext db = new DatabaseDataContext()) { Customer newCustomer = new Customer() { Email = customer.Email }; Address b = new Address() { CustomerID = newCustomer.CustomerID, Address1 = billingAddress.Address1 }; db.Customers.InsertOnSubmit(newCustomer); db.Addresses.InsertOnSubmit(b); db.SubmitChanges(); } When I run this I was hoping that the Customer and Address table automatically had the correct keys in the database since the context knows this is an auto incremented key and will do two inserts with the right key in both tables. The only way I can get this to work would be to do SubmitChanges() on the Customer object first then create the address and do SubmitChanges() on that as well. This would create two roundtrips to the database and I would like to see if I can do this in one transaction. Is it possible? Thanks

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• Partial Evaluation of ConstantExpression in ExpressionTreeVisitor

  - by Andrew Theken

  Hi all, I am not an Expression Tree master by any stretch of the imagination, what I have is code that looks like this: int external = 10; using(var session = new Session()) { session.Add(new Product { Name = "test1", Price = 20 }); session.Add(new Product {Name = "test", Price = 10}); var product = session.Products.Where(p => p.Price == external).FirstOrDefault(); Assert.Equal(10, product.Price); } Session implements all the IQueryProvider, IQueryable interfaces you'd come to expect from a LINQ Provider. When I execute the query, everything goes to plan until I read the ConstantExpression for "external", at which point, I am at a loss as to how to move forward because: //constant is ConstantExpression for "external" on the right side of the "p.Price == external" expression above. var t = constant.GetType(); //evaluates to class called "<>c__DisplayClass2" - with a member named "external" that has the value 10. The question is basically.. How can I just access the value of the member "external" - is there a way to accomplish this without using reflection? or am I cooked? What am I missing?

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• Array.BinarySearch where a certain condition is met

  - by codymanix

  I have an array of a certain type. Now I want to find an entry where a certain condition is met. What is the preferred way to do this with the restriction that I don't want to create a temporary object to find, but instead I only want to give a search condition. MyClass[] myArray; // fill and sort array.. MyClass item = Array.BinarySearch(myArray, x=>x.Name=="Joe"); // is this possible? Maybe is it possible to use LINQ to solve it?

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• Is writing eSQL database independant or not?

  - by Robert Koritnik

  Using EF we can use LINQ to read data which is rather simple (especialy using fluent calls), but we have less control unless we write eSQL on our own. Is writing eSQL database actually data store independant code? So if we decide to change data store, can the same statements still be used? Is writing eSQL strings in your code pose any serious security threats similar to writing TSQL statements in plain strings? So we moved to SPs. Could we still mode eSQL scripts outside of code as well and use some other technique to make them a bit more secure?

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• Aging Data Structure in C#

  - by thelsdj

  I want a data structure that will allow querying how many items in last X minutes. An item may just be a simple identifier or a more complex data structure, preferably the timestamp of the item will be in the item, rather than stored outside (as a hash or similar, wouldn't want to have problems with multiple items having same timestamp). So far it seems that with LINQ I could easily filter items with timestamp greater than a given time and aggregate a count. Though I'm hesitant to try to work .NET 3.5 specific stuff into my production environment yet. Are there any other suggestions for a similar data structure? The other part that I'm interested in is aging old data out, If I'm only going to be asking for counts of items less than 6 hours ago I would like anything older than that to be removed from my data structure because this may be a long-running program.

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• Problem with nested lambda expressions.

  - by Lehto

  Hey I'm trying to do a nested lambda expression like to following: textLocalizationTable.Where( z => z.SpokenLanguage.Any( x => x.FromCulture == "en-GB") ).ToList(); but i get the error: Member access 'System.String FromCulture' of 'DomainModel.Entities.SpokenLanguage' not legal on type 'System.Data.Linq.EntitySet`1[DomainModel.Entities.SpokenLanguage]. TextLocalization has this relation to spokenlanguage: [Association(OtherKey = "LocalizationID", ThisKey = "LocalizationID", Storage = "_SpokenLanguage")] private EntitySet<SpokenLanguage> _SpokenLanguage = new EntitySet<SpokenLanguage>(); public EntitySet<SpokenLanguage> SpokenLanguage { set { _SpokenLanguage = value; } get { return _SpokenLanguage; } } Any idea what is wrong?

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• Generate non-identity primary key

  - by MikeWyatt

  My workplace doesn't use identity columns or GUIDs for primary keys. Instead, we retrieve "next IDs" from a table as needed, and increment the value for each insert. Unfortunatly for me, LINQ-TO-SQL appears to be optimized around using identity columns. So I need to query and update the "NextId" table whenever I perform an insert. For simplicity, I do this immediately creating the new object. Since all operations between creation of the data context and the call to SubmitChanges are part of one transaction, do I need to create a separate data context for retrieving next IDs? Each time I need an ID, I need to query and update a table inside a transaction to prevent multiple apps from grabbing the same value. Is a separate data context the only way, or is there something better I could try?

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• How do I sign requests reliably for the Last.fm api in C#?

  - by Arda Xi

  I'm trying to implement authorization through Last.fm. I'm submitting my arguments as a Dictionary to make the signing easier. This is the code I'm using to sign my calls: public static string SignCall(Dictionary<string, string> args) { IOrderedEnumerable<KeyValuePair<string, string>> sortedArgs = args.OrderBy(arg => arg.Key); string signature = sortedArgs.Select(pair => pair.Key + pair.Value). Aggregate((first, second) => first + second); return MD5(signature + SecretKey); } I've checked the output in the debugger, it's exactly how it should be, however, I'm still getting WebExceptions every time I try. Here's my code I use to generate the URL in case it'll help: public static string GetSignedURI(Dictionary<string, string> args, bool get) { var stringBuilder = new StringBuilder(); if (get) stringBuilder.Append("http://ws.audioscrobbler.com/2.0/?"); foreach (var kvp in args) stringBuilder.AppendFormat("{0}={1}&", kvp.Key, kvp.Value); stringBuilder.Append("api_sig="+SignCall(args)); return stringBuilder.ToString(); } And sample usage to get a SessionKey: var args = new Dictionary<string, string> { {"method", "auth.getSession"}, {"api_key", ApiKey}, {"token", token} }; string url = GetSignedURI(args, true); EDIT: Oh, and the code references an MD5 function implemented like this: public static string MD5(string toHash) { byte[] textBytes = Encoding.UTF8.GetBytes(toHash); var cryptHandler = new System.Security.Cryptography.MD5CryptoServiceProvider(); byte[] hash = cryptHandler.ComputeHash(textBytes); return hash.Aggregate("", (current, a) => current + a.ToString("x2")); }

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• C# - Convert Implict Type to ObservableCollection

  - by user70192

  Hello, I have a LINQ statement that returns an implicit type. I need to get this type to be an ObservableCollection in my Silverlight 3 application. The ObservableCollection constructor in Silverlight 3 only provides an empty constructor. Because of this, I cannot directly convert my results to an ObservableCollection. Here is my code: ObservableCollection<MyTasks> visibleTasks = e.Result; var filteredResults = from visibleTask in visibleTasks select visibleTask; filteredResults = filteredResults.Where(p => p.DueDate == DateTime.Today); visibleTasks = filteredResults.ToList(); // This throws a compile time error How can I go from an implicitly typed variable to an observable collection? Thank you

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• Enumerable Contains Enumerable

  - by Tim

  For a method I have the following parameter IEnumerable<string> tags and with to query a list of objects, let's call them Post, that contains a property IEnumerable<string> Tags { get; set; }. My question is: How do I use linq to query for objects that contains all the tags from the tags parameter? private List<Post> posts = new List<Post>(); public IEnumerable<Post> GetPostsWithTags(IEnumerable<string> tags) { return ???; }

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• Treat multiple IEnumerable objects as a single IEnumerable

  - by MainMa

  Hi, My question seems to be something easy, but I can't figure it out. Let's say I have a "root" IEnumerable of objects. Each object has IEnumerable of strings. How can I obtain a single IEnumerable of those strings? A possible solution is to do: public IEnumerable<string> DoExample() { foreach (var c in rootSetOfObjects) { foreach (var n in c.childSetOfStrings) { yield return n; } } } But maybe there is a magic solution with Linq?

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• Cannot implicitly convert type System.Collection.Generic.IEnumberable

  - by Cen

  I'm receiving this error in my Linq statement --- Cannot implicitly convert type 'System.Collections.Generic.IEnumerable' to 'hcgames.ObjectClasses.ShoppingCart.ShoppingCartCartAddon'. An explicit conversion exists (are you missing a cast?) From this query ShoppingCartItems items = Cart.GetAllItems(); ShoppingCartCartAddons addons = Cart.GetAllAddons(); var stuff = from x in items select new ShoppingCartItem() { ProductID = x.ProductID, Quantity = x.Quantity, Name = x.Name, Price = x.Price, Weight = x.Weight, Addons = (from y in addons where y.ShoppingCartItemID == x.ID select y) }; I can not figure out how to cast this properly. Any suggestions? Thanks for your help!

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• IEnumerable.Cast not calling cast overload

  - by Martin Neal

  I'm not understanding something about the way .Cast works. I have an explicit (though implicit also fails) cast defined which seems to work when I use it "regularly", but not when I try to use .Cast. Why? Here is some compilable code that demonstrates my problem. public class Class1 { public string prop1 { get; set; } public int prop2 { get; set; } public static explicit operator Class2(Class1 c1) { return new Class2() { prop1 = c1.prop1, prop2 = c1.prop2 }; } } public class Class2 { public string prop1 { get; set; } public int prop2 { get; set; } } void Main() { Class1[] c1 = new Class1[] { new Class1() {prop1 = "asdf",prop2 = 1}}; //works Class2 c2 = (Class2)c1[0]; //doesn't work: Compiles, but throws at run-time //InvalidCastException: Unable to cast object of type 'Class1' to type 'Class2'. Class2 c3 = c1.Cast<Class2>().First(); }

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• Do you use enums in your data applications and how?

  - by Ivan

  My practice shows that a general enterprise application has a lot of entities which's nature corresponds to an elementary enumeration. For example We may have an Order entity which may have such fields as "OrderType", "OrderStatus", "Currency", etc. referencing corresponding Entities which are nothing more than just a textual name bound to a key to be referenced. Using enums would look very natural here. But entities have to be defined in application code at design-time, am I right? While in we need to be able to CRUD enum value variants at runtime and use enums in server-side SQL queries (like stored procedures and views). What are you practices and thoughts on this subject? I am particularly interested in C#4, linq and T-SQL.

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• Validation L2S question

  - by user158020

  This may be a bit winded because I am new to wpf. I have created a partial class for an entity in my L2S class that is primarily used for validation. It implements the onchanging and onvalidate methods. I am trying to use the MVVM pattern, and in a window/view I have set the datacontext in the xaml: <Window.DataContext> <vm:StartViewModel /> </Window.DataContext> when a user leaves a required field in the view blank, the onchanging event of the partial class is fired when I close the form, not when I save the data. So, if a user leaves the textbox blank, the old value is retained and the onchaging method is fired, but I have no idea how to alert the user of the resulting error. here is my onchanging code in the partial class: partial void Ondocument_titleChanging(string value) { if (value.Length == 0) throw new Exception("Document title is required."); if (value.Length > 256) throw new Exception("Document title cannot be longer than 256 characters."); } throwing an exception doesn't notify the user of the error. it just allows the form to close and rejects the changes to the textbox. hope this makes sense... edit: this example was taken from Scott Guthries article here: http://aspalliance.com/1427_LINQ_to_SQL_Part_5__Binding_UI_using_the_ASPLinqDataSource_Control.5

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• How can I access IEnumerable<T> extension methods on my custom subclass of BindingList<T>?

  - by Dan

  I have a custom subclass of BindingList<T> that I want to execute a LINQ query over using the handy extension methods. For example: public int GetSum(MyList<T> list) { return list.Sum(x => x.Value); } But the compiler complains that it can't resolve Sum because it doesn't recognize list as an IEnumerable<T>, which it obviously is, because this works: public int GetSum(MyList<T> list) { return ((IEnumerable<T>)list).Sum(x => x.Value); } Anyone have a clever way I can avoid the ugly and unecessary cast?

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• LINQtoSQL: Query to return List<String>

  - by ctrlShiftBryan

  I have a LINQ query that returns some object like this... var query = from c in db.Customers where ... select c; Then I do this List<String> list = new List<String>(); foreach (ProgramLanguage c in query) { //GetUL returns a String list.Add(GetUL(c.Property,c.Property2)); } Is there a way to combine into something list this? var query = from c in db.Customers where ... select new { GetUL(c.Property,c.Property2) }).ToList<String>();

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• Extraction Event

  - by Anicho

  So I have the following code: public override void Extract(object sender, ExtractionEventArgs e) { if (e.Response.HtmlDocument != null) { var myParam = e.Request.QueryStringParameters.Where(parameter => parameter.Name == QueryName).Select(parameter => parameter.Value).Distinct(); myParam. // add the extracted value to the web performance test context e.WebTest.Context.Add(this.ContextParameterName, myParam.ToString()); e.Success = true; return; } // If the extraction fails, set the error text that the user sees e.Success = false; e.Message = String.Format(CultureInfo.CurrentCulture, "Not Found: {0}", QueryName); } It's returning: System.Linq.Enumerable+<DistinctItem>d_81`1[system.string] I am expecting something along the lines of: 0152-1231-1231-123d My question is how do I extract the querystring's actual value from extractioneventargs. They say it's possible, but I have no idea.

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• LinqToSQL not updating database

  - by codegarten

  Hi. I created a database and dbml in visual studio 2010 using its wizards. Everything was working fine until i checked the tables data (also in visual studio server explorer) and none of my updates were there. using (var context = new CenasDataContext()) { context.Log = Console.Out; context.Cenas.InsertOnSubmit(new Cena() { id = 1}); context.SubmitChanges(); } This is the code i am using to update my database. At this point my database has one table with one field (PK) named ID. *INSERT INTO [dbo].Cenas VALUES (@p0) -- @p0: Input Int (Size = -1; Prec = 0; Scale = 0) [1] -- Context: SqlProvider(Sql2008) Model: AttributedMetaModel Build: 4.0.30319.1* This is LOG from the execution (printed the context log into the console). The problem i'm having is that these updates are not persistent in the database. I mean that when i query my database (visual studio server explorer - new query) i see the table is empty, every time. I am using a SQL Server database file (.mdf).

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• How to replace for-loops with a functional statement in C#?

  - by Lernkurve

  A colleague once said that God is killing a kitten every time I write a for-loop. When asked how to avoid for-loops, his answer was to use a functional language. However, if you are stuck with a non-functional language, say C#, what techniques are there to avoid for-loops or to get rid of them by refactoring? With lambda expressions and LINQ perhaps? If so, how? Questions So the question boils down to: Why are for-loops bad? Or, in what context are for-loops to avoid and why? Can you provide C# code examples of how it looks before, i.e. with a loop, and afterwards without a loop?

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• Please help me translate C# code to Ruby

  - by Valentin Vasilyev

  Here is the code: using System; using System.Collections.Generic; using System.Linq; namespace cs2 { class Program { static void Main(string[] args) { var i=Fibs.TakeWhile(x=>x < 1000).Where(x=>x % 2==0).Sum(); } static IEnumerable<long> Fibs() { long a = 0, b = 1; while (true) { yield return b; b += a; a = b - a; } } } }

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• Why does SQL Server keep throwing exceptions?

  - by Augusto Càzares

  I have my project in .NET that uses a database in SQL Server. I'm using Linq-to-SQL, sometimes when the project throws me an exception (Constraint) in a part of the project this same error keeps showing in other part of the project when I do another thing with the database. Like when I do an insertion and I had before an exception on delete the insertion throws me the delete exception, and it remains this way until I close and open again the project. My major problem is when this happen in my online project, this error in my project causes me problems in the project I'm testing online (I use the same database). I don't know if this exception is on the memory or something but its have been causing me a lot of headaches.

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