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  • Understanding LINQ to SQL (11) Performance

    - by Dixin
    [LINQ via C# series] LINQ to SQL has a lot of great features like strong typing query compilation deferred execution declarative paradigm etc., which are very productive. Of course, these cannot be free, and one price is the performance. O/R mapping overhead Because LINQ to SQL is based on O/R mapping, one obvious overhead is, data changing usually requires data retrieving:private static void UpdateProductUnitPrice(int id, decimal unitPrice) { using (NorthwindDataContext database = new NorthwindDataContext()) { Product product = database.Products.Single(item => item.ProductID == id); // SELECT... product.UnitPrice = unitPrice; // UPDATE... database.SubmitChanges(); } } Before updating an entity, that entity has to be retrieved by an extra SELECT query. This is slower than direct data update via ADO.NET:private static void UpdateProductUnitPrice(int id, decimal unitPrice) { using (SqlConnection connection = new SqlConnection( "Data Source=localhost;Initial Catalog=Northwind;Integrated Security=True")) using (SqlCommand command = new SqlCommand( @"UPDATE [dbo].[Products] SET [UnitPrice] = @UnitPrice WHERE [ProductID] = @ProductID", connection)) { command.Parameters.Add("@ProductID", SqlDbType.Int).Value = id; command.Parameters.Add("@UnitPrice", SqlDbType.Money).Value = unitPrice; connection.Open(); command.Transaction = connection.BeginTransaction(); command.ExecuteNonQuery(); // UPDATE... command.Transaction.Commit(); } } The above imperative code specifies the “how to do” details with better performance. For the same reason, some articles from Internet insist that, when updating data via LINQ to SQL, the above declarative code should be replaced by:private static void UpdateProductUnitPrice(int id, decimal unitPrice) { using (NorthwindDataContext database = new NorthwindDataContext()) { database.ExecuteCommand( "UPDATE [dbo].[Products] SET [UnitPrice] = {0} WHERE [ProductID] = {1}", id, unitPrice); } } Or just create a stored procedure:CREATE PROCEDURE [dbo].[UpdateProductUnitPrice] ( @ProductID INT, @UnitPrice MONEY ) AS BEGIN BEGIN TRANSACTION UPDATE [dbo].[Products] SET [UnitPrice] = @UnitPrice WHERE [ProductID] = @ProductID COMMIT TRANSACTION END and map it as a method of NorthwindDataContext (explained in this post):private static void UpdateProductUnitPrice(int id, decimal unitPrice) { using (NorthwindDataContext database = new NorthwindDataContext()) { database.UpdateProductUnitPrice(id, unitPrice); } } As a normal trade off for O/R mapping, a decision has to be made between performance overhead and programming productivity according to the case. In a developer’s perspective, if O/R mapping is chosen, I consistently choose the declarative LINQ code, unless this kind of overhead is unacceptable. Data retrieving overhead After talking about the O/R mapping specific issue. Now look into the LINQ to SQL specific issues, for example, performance in the data retrieving process. The previous post has explained that the SQL translating and executing is complex. Actually, the LINQ to SQL pipeline is similar to the compiler pipeline. It consists of about 15 steps to translate an C# expression tree to SQL statement, which can be categorized as: Convert: Invoke SqlProvider.BuildQuery() to convert the tree of Expression nodes into a tree of SqlNode nodes; Bind: Used visitor pattern to figure out the meanings of names according to the mapping info, like a property for a column, etc.; Flatten: Figure out the hierarchy of the query; Rewrite: for SQL Server 2000, if needed Reduce: Remove the unnecessary information from the tree. Parameterize Format: Generate the SQL statement string; Parameterize: Figure out the parameters, for example, a reference to a local variable should be a parameter in SQL; Materialize: Executes the reader and convert the result back into typed objects. So for each data retrieving, even for data retrieving which looks simple: private static Product[] RetrieveProducts(int productId) { using (NorthwindDataContext database = new NorthwindDataContext()) { return database.Products.Where(product => product.ProductID == productId) .ToArray(); } } LINQ to SQL goes through above steps to translate and execute the query. Fortunately, there is a built-in way to cache the translated query. Compiled query When such a LINQ to SQL query is executed repeatedly, The CompiledQuery can be used to translate query for one time, and execute for multiple times:internal static class CompiledQueries { private static readonly Func<NorthwindDataContext, int, Product[]> _retrieveProducts = CompiledQuery.Compile((NorthwindDataContext database, int productId) => database.Products.Where(product => product.ProductID == productId).ToArray()); internal static Product[] RetrieveProducts( this NorthwindDataContext database, int productId) { return _retrieveProducts(database, productId); } } The new version of RetrieveProducts() gets better performance, because only when _retrieveProducts is first time invoked, it internally invokes SqlProvider.Compile() to translate the query expression. And it also uses lock to make sure translating once in multi-threading scenarios. Static SQL / stored procedures without translating Another way to avoid the translating overhead is to use static SQL or stored procedures, just as the above examples. Because this is a functional programming series, this article not dive into. For the details, Scott Guthrie already has some excellent articles: LINQ to SQL (Part 6: Retrieving Data Using Stored Procedures) LINQ to SQL (Part 7: Updating our Database using Stored Procedures) LINQ to SQL (Part 8: Executing Custom SQL Expressions) Data changing overhead By looking into the data updating process, it also needs a lot of work: Begins transaction Processes the changes (ChangeProcessor) Walks through the objects to identify the changes Determines the order of the changes Executes the changings LINQ queries may be needed to execute the changings, like the first example in this article, an object needs to be retrieved before changed, then the above whole process of data retrieving will be went through If there is user customization, it will be executed, for example, a table’s INSERT / UPDATE / DELETE can be customized in the O/R designer It is important to keep these overhead in mind. Bulk deleting / updating Another thing to be aware is the bulk deleting:private static void DeleteProducts(int categoryId) { using (NorthwindDataContext database = new NorthwindDataContext()) { database.Products.DeleteAllOnSubmit( database.Products.Where(product => product.CategoryID == categoryId)); database.SubmitChanges(); } } The expected SQL should be like:BEGIN TRANSACTION exec sp_executesql N'DELETE FROM [dbo].[Products] AS [t0] WHERE [t0].[CategoryID] = @p0',N'@p0 int',@p0=9 COMMIT TRANSACTION Hoverer, as fore mentioned, the actual SQL is to retrieving the entities, and then delete them one by one:-- Retrieves the entities to be deleted: exec sp_executesql N'SELECT [t0].[ProductID], [t0].[ProductName], [t0].[SupplierID], [t0].[CategoryID], [t0].[QuantityPerUnit], [t0].[UnitPrice], [t0].[UnitsInStock], [t0].[UnitsOnOrder], [t0].[ReorderLevel], [t0].[Discontinued] FROM [dbo].[Products] AS [t0] WHERE [t0].[CategoryID] = @p0',N'@p0 int',@p0=9 -- Deletes the retrieved entities one by one: BEGIN TRANSACTION exec sp_executesql N'DELETE FROM [dbo].[Products] WHERE ([ProductID] = @p0) AND ([ProductName] = @p1) AND ([SupplierID] IS NULL) AND ([CategoryID] = @p2) AND ([QuantityPerUnit] IS NULL) AND ([UnitPrice] = @p3) AND ([UnitsInStock] = @p4) AND ([UnitsOnOrder] = @p5) AND ([ReorderLevel] = @p6) AND (NOT ([Discontinued] = 1))',N'@p0 int,@p1 nvarchar(4000),@p2 int,@p3 money,@p4 smallint,@p5 smallint,@p6 smallint',@p0=78,@p1=N'Optimus Prime',@p2=9,@p3=$0.0000,@p4=0,@p5=0,@p6=0 exec sp_executesql N'DELETE FROM [dbo].[Products] WHERE ([ProductID] = @p0) AND ([ProductName] = @p1) AND ([SupplierID] IS NULL) AND ([CategoryID] = @p2) AND ([QuantityPerUnit] IS NULL) AND ([UnitPrice] = @p3) AND ([UnitsInStock] = @p4) AND ([UnitsOnOrder] = @p5) AND ([ReorderLevel] = @p6) AND (NOT ([Discontinued] = 1))',N'@p0 int,@p1 nvarchar(4000),@p2 int,@p3 money,@p4 smallint,@p5 smallint,@p6 smallint',@p0=79,@p1=N'Bumble Bee',@p2=9,@p3=$0.0000,@p4=0,@p5=0,@p6=0 -- ... COMMIT TRANSACTION And the same to the bulk updating. This is really not effective and need to be aware. Here is already some solutions from the Internet, like this one. The idea is wrap the above SELECT statement into a INNER JOIN:exec sp_executesql N'DELETE [dbo].[Products] FROM [dbo].[Products] AS [j0] INNER JOIN ( SELECT [t0].[ProductID], [t0].[ProductName], [t0].[SupplierID], [t0].[CategoryID], [t0].[QuantityPerUnit], [t0].[UnitPrice], [t0].[UnitsInStock], [t0].[UnitsOnOrder], [t0].[ReorderLevel], [t0].[Discontinued] FROM [dbo].[Products] AS [t0] WHERE [t0].[CategoryID] = @p0) AS [j1] ON ([j0].[ProductID] = [j1].[[Products])', -- The Primary Key N'@p0 int',@p0=9 Query plan overhead The last thing is about the SQL Server query plan. Before .NET 4.0, LINQ to SQL has an issue (not sure if it is a bug). LINQ to SQL internally uses ADO.NET, but it does not set the SqlParameter.Size for a variable-length argument, like argument of NVARCHAR type, etc. So for two queries with the same SQL but different argument length:using (NorthwindDataContext database = new NorthwindDataContext()) { database.Products.Where(product => product.ProductName == "A") .Select(product => product.ProductID).ToArray(); // The same SQL and argument type, different argument length. database.Products.Where(product => product.ProductName == "AA") .Select(product => product.ProductID).ToArray(); } Pay attention to the argument length in the translated SQL:exec sp_executesql N'SELECT [t0].[ProductID] FROM [dbo].[Products] AS [t0] WHERE [t0].[ProductName] = @p0',N'@p0 nvarchar(1)',@p0=N'A' exec sp_executesql N'SELECT [t0].[ProductID] FROM [dbo].[Products] AS [t0] WHERE [t0].[ProductName] = @p0',N'@p0 nvarchar(2)',@p0=N'AA' Here is the overhead: The first query’s query plan cache is not reused by the second one:SELECT sys.syscacheobjects.cacheobjtype, sys.dm_exec_cached_plans.usecounts, sys.syscacheobjects.[sql] FROM sys.syscacheobjects INNER JOIN sys.dm_exec_cached_plans ON sys.syscacheobjects.bucketid = sys.dm_exec_cached_plans.bucketid; They actually use different query plans. Again, pay attention to the argument length in the [sql] column (@p0 nvarchar(2) / @p0 nvarchar(1)). Fortunately, in .NET 4.0 this is fixed:internal static class SqlTypeSystem { private abstract class ProviderBase : TypeSystemProvider { protected int? GetLargestDeclarableSize(SqlType declaredType) { SqlDbType sqlDbType = declaredType.SqlDbType; if (sqlDbType <= SqlDbType.Image) { switch (sqlDbType) { case SqlDbType.Binary: case SqlDbType.Image: return 8000; } return null; } if (sqlDbType == SqlDbType.NVarChar) { return 4000; // Max length for NVARCHAR. } if (sqlDbType != SqlDbType.VarChar) { return null; } return 8000; } } } In this above example, the translated SQL becomes:exec sp_executesql N'SELECT [t0].[ProductID] FROM [dbo].[Products] AS [t0] WHERE [t0].[ProductName] = @p0',N'@p0 nvarchar(4000)',@p0=N'A' exec sp_executesql N'SELECT [t0].[ProductID] FROM [dbo].[Products] AS [t0] WHERE [t0].[ProductName] = @p0',N'@p0 nvarchar(4000)',@p0=N'AA' So that they reuses the same query plan cache: Now the [usecounts] column is 2.

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  • An abundance of LINQ queries and expressions using both the query and method syntax.

    - by nikolaosk
    In this post I will be writing LINQ queries against an array of strings, an array of integers.Moreover I will be using LINQ to query an SQL Server database. I can use LINQ against arrays since the array of strings/integers implement the IENumerable interface. I thought it would be a good idea to use both the method syntax and the query syntax. There are other places on the net where you can find examples of LINQ queries but I decided to create a big post using as many LINQ examples as possible. We...(read more)

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  • What is Linq?

    - by Aamir Hasan
    The way data can be retrieved in .NET. LINQ provides a uniform way to retrieve data from any object that implements the IEnumerable<T> interface. With LINQ, arrays, collections, relational data, and XML are all potential data sources. Why LINQ?With LINQ, you can use the same syntax to retrieve data from any data source:var query = from e in employeeswhere e.id == 1select e.nameThe middle level represents the three main parts of the LINQ project: LINQ to Objects is an API that provides methods that represent a set of standard query operators (SQOs) to retrieve data from any object whose class implements the IEnumerable<T> interface. These queries are performed against in-memory data.LINQ to ADO.NET augments SQOs to work against relational data. It is composed of three parts.LINQ to SQL (formerly DLinq) is use to query relational databases such as Microsoft SQL Server. LINQ to DataSet supports queries by using ADO.NET data sets and data tables. LINQ to Entities is a Microsoft ORM solution, allowing developers to use Entities (an ADO.NET 3.0 feature) to declaratively specify the structure of business objects and use LINQ to query them. LINQ to XML (formerly XLinq) not only augments SQOs but also includes a host of XML-specific features for XML document creation and queries. What You Need to Use LINQLINQ is a combination of extensions to .NET languages and class libraries that support them. To use it, you’ll need the following: Obviously LINQ, which is available from the new Microsoft .NET Framework 3.5 that you can download at http://go.microsoft.com/?linkid=7755937.You can speed up your application development time with LINQ using Visual Studio 2008, which offers visual tools such as LINQ to SQL designer and the Intellisense  support with LINQ’s syntax.Optionally, you can download the Visual C# 2008 Expression Edition tool at www.microsoft.com/vstudio/express/download. It is the free edition of Visual Studio 2008 and offers a lot of LINQ support such as Intellisense and LINQ to SQL designer. To use LINQ to ADO.NET, you need SQL

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  • Exception with Linq2SQL Query

    - by Hadi Eskandari
    I am running a query using Linq2SQL that comes down to following query: DateTime? expiration = GetExpirationDate(); IQueryable<Persons> persons = GetPersons(); IQueryable<Items> subquery = from i in db.Items where i.ExpirationDate >= expiration select i; return persons.Where(p = p.Items != null && p.Items.Any(item => subquery.Contains(item))); When I evaluate the result of the function, I get a NullReferenceException and here's the stack trace. Any idea what I'm doing wrong?! Basically I want to select all the persons and filter them by item expiration date. at System.Data.Linq.SqlClient.SqlFactory.Member(SqlExpression expr, MemberInfo member) at System.Data.Linq.SqlClient.QueryConverter.VisitMemberAccess(MemberExpression ma) at System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node) at System.Data.Linq.SqlClient.QueryConverter.Visit(Expression node) at System.Data.Linq.SqlClient.QueryConverter.VisitExpression(Expression exp) at System.Data.Linq.SqlClient.QueryConverter.VisitBinary(BinaryExpression b) at System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node) at System.Data.Linq.SqlClient.QueryConverter.Visit(Expression node) at System.Data.Linq.SqlClient.QueryConverter.VisitExpression(Expression exp) at System.Data.Linq.SqlClient.QueryConverter.VisitBinary(BinaryExpression b) at System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node) at System.Data.Linq.SqlClient.QueryConverter.Visit(Expression node) at System.Data.Linq.SqlClient.QueryConverter.VisitExpression(Expression exp) at System.Data.Linq.SqlClient.QueryConverter.VisitWhere(Expression sequence, LambdaExpression predicate) at System.Data.Linq.SqlClient.QueryConverter.VisitSequenceOperatorCall(MethodCallExpression mc) at System.Data.Linq.SqlClient.QueryConverter.VisitMethodCall(MethodCallExpression mc) at System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node) at System.Data.Linq.SqlClient.QueryConverter.Visit(Expression node) at System.Data.Linq.SqlClient.QueryConverter.VisitContains(Expression sequence, Expression value) at System.Data.Linq.SqlClient.QueryConverter.VisitSequenceOperatorCall(MethodCallExpression mc) at System.Data.Linq.SqlClient.QueryConverter.VisitMethodCall(MethodCallExpression mc) at System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node) at System.Data.Linq.SqlClient.QueryConverter.Visit(Expression node) at System.Data.Linq.SqlClient.QueryConverter.VisitExpression(Expression exp) at System.Data.Linq.SqlClient.QueryConverter.VisitQuantifier(SqlSelect select, LambdaExpression lambda, Boolean isAny) at System.Data.Linq.SqlClient.QueryConverter.VisitSequenceOperatorCall(MethodCallExpression mc) at System.Data.Linq.SqlClient.QueryConverter.VisitMethodCall(MethodCallExpression mc) at System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node) at System.Data.Linq.SqlClient.QueryConverter.Visit(Expression node) at System.Data.Linq.SqlClient.QueryConverter.VisitExpression(Expression exp) at System.Data.Linq.SqlClient.QueryConverter.VisitBinary(BinaryExpression b) at System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node) at System.Data.Linq.SqlClient.QueryConverter.Visit(Expression node) at System.Data.Linq.SqlClient.QueryConverter.VisitExpression(Expression exp) at System.Data.Linq.SqlClient.QueryConverter.VisitWhere(Expression sequence, LambdaExpression predicate) at System.Data.Linq.SqlClient.QueryConverter.VisitSequenceOperatorCall(MethodCallExpression mc) at System.Data.Linq.SqlClient.QueryConverter.VisitMethodCall(MethodCallExpression mc) at System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node) at System.Data.Linq.SqlClient.QueryConverter.ConvertOuter(Expression node) at System.Data.Linq.SqlClient.SqlProvider.BuildQuery(Expression query, SqlNodeAnnotations annotations) at System.Data.Linq.SqlClient.SqlProvider.System.Data.Linq.Provider.IProvider.Execute(Expression query) at System.Data.Linq.DataQuery`1.System.Collections.Generic.IEnumerable.GetEnumerator() at System.Linq.SystemCore_EnumerableDebugView`1.get_Items()

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  • How to create a dynamic Linq Join extension method

    - by Royd Brayshay
    There was a library of dynamic Linq extensions methods released as a sample with VS2008. I'd like to extend it with a Join method. The code below fails with a parameter miss match exception at run time. Can anyone find the problem? public static IQueryable Join(this IQueryable outer, IEnumerable inner, string outerSelector, string innerSelector, string resultsSelector, params object[] values) { if (inner == null) throw new ArgumentNullException("inner"); if (outerSelector == null) throw new ArgumentNullException("outerSelector"); if (innerSelector == null) throw new ArgumentNullException("innerSelector"); if (resultsSelector == null) throw new ArgumentNullException("resultsSelctor"); LambdaExpression outerSelectorLambda = DynamicExpression.ParseLambda(outer.ElementType, null, outerSelector, values); LambdaExpression innerSelectorLambda = DynamicExpression.ParseLambda(inner.AsQueryable().ElementType, null, innerSelector, values); ParameterExpression[] parameters = new ParameterExpression[] { Expression.Parameter(outer.ElementType, "outer"), Expression.Parameter(inner.AsQueryable().ElementType, "inner") }; LambdaExpression resultsSelectorLambda = DynamicExpression.ParseLambda(parameters, null, resultsSelector, values); return outer.Provider.CreateQuery( Expression.Call( typeof(Queryable), "Join", new Type[] { outer.ElementType, inner.AsQueryable().ElementType, outerSelectorLambda.Body.Type, innerSelectorLambda.Body.Type, resultsSelectorLambda.Body.Type }, outer.Expression, inner.AsQueryable().Expression, Expression.Quote(outerSelectorLambda), Expression.Quote(innerSelectorLambda), Expression.Quote(resultsSelectorLambda))); } I've now fixed it myself, here's the answer. Please vote it up or add a better one.

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  • Is LINQ to SQL deprecated?

    - by Mayo
    Back in late 2008 there was alot of debate about the future of LINQ to SQL. Many suggested that Microsoft's investments in the Entity Framework in .NET 4.0 were a sign that LINQ to SQL had no future. I figured I'd wait before making my own decision since folks were not in agreement. Fast-forward 18 months and I've got vendors providing solutions that rely on LINQ to SQL and I have personally given it a try and really enjoyed working with it. I figured it was here to stay. But I'm reading a new book (C# 4.0 How-To by Ben Watson) and in chapter 21 (LINQ), he suggests that it "has been more or less deprecated by Microsoft" and suggests using LINQ to Entity Framework. My question to you is whether or not LINQ to SQL is officially deprecated and/or if authoritative entities (Microsoft, Scott Gu, etc.) officially suggest using LINQ to Entities instead of LINQ to SQL.

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  • Short-circuit evaluation and LINQ-to-NHibernate

    - by afsharm
    It seems that LINQ-to-NHibernate and LINQ-to-SQL does not support short-circuit evaluation in where clause of query. Am I right? Is there any workaround? May it be added to next versions of LINQ-to-NHibernate and LINQ-to-SQL? for more information plz see followings: http://stackoverflow.com/questions/772261/the-or-operator-in-linq-with-c http://stackoverflow.com/questions/2306302/why-ordinary-laws-in-evaluting-boolean-expression-does-not-fit-into-linq

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  • Linq Tutorial

    - by SAMIR BHOGAYTA
    Microsoft LINQ Tutorials http://www.deitel.com/ResourceCenters/Programming/MicrosoftLINQ/Tutorials/tabid/2673/Default.aspx Introducing C# 3 – Part 4 LINQ http://www.programmersheaven.com/2/CSharp3-4 101 LINQ Samples http://msdn.microsoft.com/en-us/vcsharp/aa336746.aspx What is LinQ http://www.dotnetspider.com/forum/173039-what-linq-net.aspx Beginners Guides http://www.progtalk.com/viewarticle.aspx?articleid=68 http://www.programmersheaven.com/2/CSharp3-4 http://dotnetslackers.com/articles/csharp/introducinglinq1.aspx Using Linq http://weblogs.asp.net/scottgu/archive/2006/05/14/446412.aspx Step By Step Articles http://www.codeproject.com/KB/linq/linqtutorial.aspx http://www.codeproject.com/KB/linq/linqtutorial2.aspx http://www.codeproject.com/KB/linq/linqtutorial3.aspx

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  • Linq To SQL: Behaviour for table field which is NotNull and having Default value or binding

    - by kaushalparik27
    I found this something interesting while wandering over community which I would like to share. The post is whole about: DBML is not considering the table field's "Default value or Binding" setting which is a NotNull. I mean the field which can not be null but having default value set needs to be set IsDbGenerated = true in DBML file explicitly.Consider this situation: There is a simple tblEmployee table with below structure: The fields are simple. EmployeeID is a Primary Key with Identity Specification = True with Identity Seed = 1 to autogenerate numeric value for this field. EmployeeName and their EmailAddress to store in rest of 2 fields. And the last one is "DateAdded" with DateTime datatype which doesn't allow NULL but having Default Value/Binding with "GetDate()". That means if we don't pass any value to this field then SQL will insert current date in "DateAdded" field.So, I start with a new website, add a DBML file and dropped the said table to generate LINQ To SQL context class. Finally, I write a simple code snippet to insert data into the tblEmployee table; BUT, I am not passing any value to "DateAdded" field. Because I am considering SQL Server's "Default Value or Binding (GetDate())" setting to this field and understand that SQL will insert current date to this field.        using (TestDatabaseDataContext context = new TestDatabaseDataContext())        {            tblEmployee tblEmpObjet = new tblEmployee();            tblEmpObjet.EmployeeName = "KaushaL";            tblEmpObjet.EmployeeEmailAddress = "[email protected]";            context.tblEmployees.InsertOnSubmit(tblEmpObjet);            context.SubmitChanges();        }Here comes the twist when application give me below error:  This is something not expecting! From the error it clearly depicts that LINQ is passing NULL value to "DateAdded" Field while according to my understanding it should respect Sql Server's "Default value or Binding" setting for this field. A bit googling and I found very interesting related to this problem.When we set Primary Key to any field with "Identity Specification" Property set to true; DBML set one important property "IsDbGenerated=true" for this field. BUT, when we set "Default Value or Biding" property for some field; we need to explicitly tell the DBML/LINQ to let it know that this field is having default binding at DB side that needs to be respected if I don't pass any value. So, the solution is: You need to explicitly set "IsDbGenerated=true" for such field to tell the LINQ that the field is having default value or binding at Sql Server side so, please don't worry if i don't pass any value for it.You can select the field and set this property from property window in DBML Designer file or write the property in DBML.Designer.cs file directly. I have attached a working example with required table script with this post here. I hope this would be helpful for someone hunting for the same. Happy Discovery!

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  • My "Ah-Ha!" Moment With LINQ

    - by CompiledMonkey
    I'm currently working on a set of web services that will be consumed by iPhone and Android devices. Given how often the web services will be called in a relatively short period of time, the data access for the web services has proven to be a very important aspect of the project. In choosing the technology stack for implementation, I opted for LINQ to SQL as it was something I had dabbled with in the past and wanted to learn more about in a real environment. The query optimization happening behind...(read more)

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  • Simple way to return anonymous types (to make MVC using LINQ possible)

    - by BlueRaja The Green Unicorn
    I'd like to implement MVC while using LINQ (specifically, LINQ-to-entities). The way I would do this is have the Controller generate (or call something which generates) the result-set using LINQ, then return that to the View to display the data. The problem is, if I do: return (from o in myTable select o); All the columns are read from the database, even the ones (potentially dozens) I don't want. And - more importantly - I can't do something like this: return (from o in myTable select new { o.column }); because there is no way to make anonymous types type-safe! I know for sure there is no nice, clean way of doing this in 3.5 (this is not clean...), but what about 4.0? Is there anything planned, or even proposed? Without something like duck-typing-for-LINQ, or type-safe anonymous return values (it seems to me the compiler should certainly be capable of that), it appears to be nearly impossible to cleanly separate the Controller from the View.

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  • Using LINQ to fetch result from nested SQL queries

    - by Shantanu Gupta
    This is my first question and first day in Linq so bit difficult day for me to understand. I want to fetch some records from database i.e. select * from tblDepartment where department_id in ( select department_id from tblMap where Guest_Id = @GuestId ) I have taken two DataTable. i.e. tblDepartment, tblMap Now I want to fetch this result and want to store it in third DataTable. How can I do this. I have been able to construct this query up till now after googling. var query = from myrow in _dtDepartment.AsEnumerable() where myrow.Field<int>("Department_Id") == _departmentId select myrow; Please provide me some link for learning Linq mainly for DataTables and DataSets. EDIT: I have got a very similar example here but i m still not able to understand how it is working. Please put some torch on it.

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  • LINQ to Entities pulling back entire table

    - by Focus
    In my application I'm pulling back a user's "feed". This contains all of that user's activities, events, friend requests from other users, etc. When I pull back the feed I'm calling various functions to filter the request along the way. var userFeed = GetFeed(db); // Query to pull back all data userFeed = FilterByUser(userFeed, user, db); // Filter for the user userFeed = SortFeed(userFeed, page, sortBy, typeName); // Sort it The data that is returned is exactly what I need, however when I look at a SQL Profile Trace I can see that the query that is getting this data does not filter it at the database level and instead is selecting ALL data in the table(s). This query does not execute until I iterate through the results on my view. All of these functions return an IEnumerable object. I was under the impression that LINQ would take all of my filters and form one query to pull back the data I want instead of pulling back all the data and then filtering it on the server. What am I doing wrong or what don't I understand about the way LINQ evaluates queries?

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  • How can I do this with LINQ?

    - by Liam
    All I'm after doing is this: SELECT CallTypeID, Count(CallTypeID) as NumberOfCalls FROM [Helpdesk_HR].[dbo].[CallHeader] WHERE CallHeader.DateOpened <= GETDATE()-7 GROUP BY CallTypeID in LINQ. But I can't work out a way of doing it and getting it to work. I would use Linqer, but my company won't pay for it at present. Any help is greatly appreciated as I'm sure the answer is obvious. It's just been one of those days today.

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  • LINQ Query Help!

    - by rk1962
    Can someone hep me converting the following SQL query into LINQ? select convert(varchar(10),date,110) as 'Date', max(users) as 'Maximum Number of Users', max(transactions) as 'Maximum Number of Transactions' from stats where datepart(Year, Date) = '2010' group by convert(varchar(10),date,110) order by convert(varchar(10),date,110) Thank you in advance!

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  • Method 'SingleOrDefault' not supported by Linq to Entities

    - by user300992
    I read other posts on similar problem on using SingleOfDefault on Linq-To-Entity, some suggested using "First()" and some others suggested using "Extension" method to implement the Single(). This code throws exception: Movie movie = (from a in movies where a.MovieID == '12345' select a).SingleOrDefault(); If I convert the object query to a List using .ToList(), "SingleOrDefault()" actually works perfectly without throwing any error. My question is: Is it not good to convert to List? Is it going to be performance issue for more complicated queries? What does it get translated in SQL? Movie movie = (from a in movies.ToList() where a.MovieID == '12345' select a).SingleOrDefault();

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  • Use Any() and Count() in Dynamic Linq

    - by ArpanDesai
    I am trying to write dynamic Linq Library query to fetch record on condition, Customers who has order count is greater than 3 and ShipVia field equal 2. Below is my syntax what i have tried. object[] objArr = new object[10]; objArr[0] = 1; IQueryable<Customer> test = db.Customers.Where("Orders.Count(ShipVia=2)", objArr); and IQueryable<Customer> test = db.Customers.Where("Orders.Any(ShipVia=2).Count()", objArr); But both are not working. In second query Any returns true so it won't work with Count. Suggest me a way to implement this.

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  • return from a linq where statement

    - by Vaccano
    I have the following link function MyLinqToSQLTable.Where(x => x.objectID == paramObjectID).ToList(); I most of the time you can change a linq call to be several lines by adding curly brackets around the method body. Like this: MyLinqToSQLTable.Where(x => { x.objectID == paramObjectID; }).ToList(); Problem is the implied return that was there when I just did a Boolean compare is now not done. Return (x.objectID == paramObjectID); is not accepted either. How do do this? can I do this? NOTE: I know that I can add another where clause if needed. But I would still like to know the answer to this.

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  • Parse XML tree with no id using LINQ to XML

    - by Danny
    Requirement I want to read a XML tree, fill my objects with encountered attributes and after every run a method (insert it into my db). The amount of parents is not specified, also the order is not specified, it could be, address-death-death-address-address for example Input file Overview: <Root> <Element> <Element2> <Parent> <Child> <Grandchild> <Grandchild> </Child> </Parent> </Element2> </Element1> </Root> Full example: <?xml version="1.0" encoding="utf-8" ?> <Root> <Element1> <Element2> <Parent> <Child> <Grandchild> <number>01</number> <name>Person</name> <Rows> <Row> <number>0110</number> <name>ID</name> <value>123456789</value> </Row> </Rows> </Grandchild> <Grandchild> <number>08</number> <name>Address</name> <Rows> <Row> <number>1110</number> <name>street</name> <value>first aveneu</value> </Row> <Row> <number>1120</number> <name>streetnumber</name> <value>345</value> </Row> <Row> <number>1130</number> <name>zip</name> <value>2938PS</value> </Row> <Row> <number>1160</number> <name>country</name> <value>Germany</value> </Row> </Rows> </Grandchild> </Child> </Parent> <Parent> <Child> <Grandchild> <number>01</number> <name>Person</name> <Rows> <Row> <number>0110</number> <name>ID</name> <value>987654321</value> </Row> </Rows> </Grandchild> <Grandchild> <number>06</number> <name>Death</name> <Rows> <Row> <number>0810</number> <name>date</name> <value>2012-01-03</value> </Row> <Row> <number>0820</number> <name>placeOfDeath</name> <value>attic</value> </Row> <Row> <number>0830</number> <name>funeral</name> <value>burrial</value> </Row> </Rows> </Grandchild> </Child> </Parent> </Element2> </Element1> </Root> Desired result After encounter of parent determine type of grandchild (number 6 is death number 8 is address) Every parent has ALWAYS grandchild number 1 'Person', the second grandchild is either death or address. reading first parent Person person = new Person(); person.ID = value; <--- filled with 123456789 person.street = value; <--- filled with first aveneu person.streetnumber = value; <--- filled with 345 person.zip = value; <--- filled with 2938PS person.country = value; <--- filled with germany person.DoMethod(); // inserts the value in db Continue reading next parent. Person person = new Person(); person.ID = value; <--- filled with 987654321 person.date = value; <--- filled with 2012-01-03 person.placeOfDeath = value; <--- filled with attic person.funeral = value; <--- filled with burrial person.DoMethod(); // insert the values in db Continue reading till no parents found EDIT: how do I target the name element of the second grandchild for every child? Like address or death Code/Credit I got no further then this, with help of Daniel Hilgarth: Linq to XML (C#) parse XML tree with no attributes/id to object The XML tree has changed, and I am really stuck.. in the meantime I try to post new working code...

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  • Why I am getting Null from this statement. Query Syntax in C#

    - by Shantanu Gupta
    This is not working. Returns Null to dept_list. var dept_list = ((from map in DtMapGuestDepartment.AsEnumerable() where map.Field<Nullable<long>>("Guest_Id") == 174 select map.Field<Nullable<long>>("Department_id")).Distinct())as IEnumerable<DataRow>; DataTable dt = dept_list.CopyToDataTable(); //dept_list comes null here This works as desired. var dept_list = from map in DtMapGuestDepartment.AsEnumerable() where map.Field<Nullable<long>>("Guest_Id") == 174 select map; DataTable dt = dept_list.CopyToDataTable(); //when used like this runs correct. What mistake is being done by me here. ?

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