Queryable.First<TSource> Method (IQueryable<TSource>)

Returns the first element of a sequence.

Namespace:  System.Linq
Assembly:  System.Core (in System.Core.dll)

Syntax

'Declaration
<ExtensionAttribute> _
Public Shared Function First(Of TSource) ( _
    source As IQueryable(Of TSource) _
) As TSource
public static TSource First<TSource>(
    this IQueryable<TSource> source
)

Type Parameters

  • TSource
    The type of the elements of source.

Parameters

Return Value

Type: TSource
The first element in 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.

Exceptions

Exception Condition
ArgumentNullException

source is nulla null reference (Nothing in Visual Basic).

InvalidOperationException

The source sequence is empty.

Remarks

The First<TSource>(IQueryable<TSource>) method generates a MethodCallExpression that represents calling First<TSource>(IQueryable<TSource>) itself as a constructed generic method. It then passes the MethodCallExpression to the Execute<TResult>(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 First<TSource>(IQueryable<TSource>) depends on the implementation of the type of the source parameter. The expected behavior is that it returns the first element in source.

Examples

The following code example demonstrates how to use First<TSource>(IQueryable<TSource>) to return the first element in a sequence.

Dim numbers() As Integer = {9, 34, 65, 92, 87, 435, 3, 54, _
                    83, 23, 87, 435, 67, 12, 19}

Dim first As Integer = numbers.AsQueryable().First()

outputBlock.Text &= first & vbCrLf

' This code produces the following output:
'
' 9
         int[] numbers = { 9, 34, 65, 92, 87, 435, 3, 54, 
                                83, 23, 87, 435, 67, 12, 19 };

         int first = numbers.AsQueryable().First();

         outputBlock.Text += first + "\n";

         /*
             This code produces the following output:

             9
         */

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.