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

 

Returns the first element of a sequence.

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

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

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.

Type Parameters

TSource

The type of the elements of source.

Exception Condition
ArgumentNullException

source is null.

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

Universal Windows Platform
Available since 4.5
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.1
Windows Phone
Available since 8.1
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