Queryable.Select<TSource, TResult> Method (IQueryable<TSource>, Expression<Func<TSource, TResult>>)
Projects each element of a sequence into a new form.
Namespace: System.Linq
Assembly: System.Core (in System.Core.dll)
public static IQueryable<TResult> Select<TSource, TResult>( this IQueryable<TSource> source, Expression<Func<TSource, TResult>> selector )
Type Parameters
- TSource
The type of the elements of source.
- TResult
The type of the value returned by the function represented by selector.
Parameters
- source
- Type: System.Linq.IQueryable<TSource>
A sequence of values to project.
- selector
- Type: System.Linq.Expressions.Expression<Func<TSource, TResult>>
A projection function to apply to each element.
Return Value
Type: System.Linq.IQueryable<TResult>An IQueryable<T> whose elements are the result of invoking a projection function on each element of source.
Usage Note
In Visual Basic and C#, you can call this method as an instance method on any object of type IQueryable<TSource>. When you use instance method syntax to call this method, omit the first parameter. For more information, see Extension Methods (Visual Basic) or Extension Methods (C# Programming Guide).| Exception | Condition |
|---|---|
| ArgumentNullException | source or selector is null. |
This method has at least one parameter of type Expression<TDelegate> whose type argument is one of the Func<T, TResult> types. For these parameters, you can pass in a lambda expression and it will be compiled to an Expression<TDelegate>.
The Select<TSource, TResult>(IQueryable<TSource>, Expression<Func<TSource, TResult>>) method generates a MethodCallExpression that represents calling Select<TSource, TResult>(IQueryable<TSource>, Expression<Func<TSource, TResult>>) itself as a constructed generic method. It then passes the MethodCallExpression to the CreateQuery(Expression) method of the IQueryProvider represented by the Provider property of the source parameter.
The query behavior that occurs as a result of executing an expression tree that represents calling Select<TSource, TResult>(IQueryable<TSource>, Expression<Func<TSource, TResult>>) depends on the implementation of the type of the source parameter. The expected behavior is that it invokes selector on each element of source to project it into a different form.
The following code example demonstrates how to use Select<TSource, TResult>(IQueryable<TSource>, Expression<Func<TSource, TResult>>) to project over a sequence of values.
List<int> range =
new List<int> { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
// Project the square of each int value.
IEnumerable<int> squares =
range.AsQueryable().Select(x => x * x);
foreach (int num in squares)
Console.WriteLine(num);
/*
This code produces the following output:
1
4
9
16
25
36
49
64
81
100
*/
Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
