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Queryable.First(Of TSource) Method (IQueryable(Of TSource))

Returns the first element of a sequence.

Namespace:  System.Linq
Assemblies:   System.Linq.Queryable (in System.Linq.Queryable.dll)
  System.Core (in System.Core.dll)

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

Type Parameters

TSource

The type of the elements of source.

Parameters

source
Type: System.Linq.IQueryable(Of TSource)

The IQueryable(Of T) to return the first element of.

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(Of 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).

ExceptionCondition
ArgumentNullException

source is Nothing.

InvalidOperationException

The source sequence is empty.

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

The following code example demonstrates how to use First(Of TSource)(IQueryable(Of 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()

        MsgBox(first)

        ' This code produces the following output: 
        
        ' 9

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8
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