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

Returns an Int64 that represents the total number of elements in a sequence.

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

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

Type Parameters

TSource

The type of the elements of source.

Parameters

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

An IQueryable(Of T) that contains the elements to be counted.

Return Value

Type: System.Int64
The number of elements 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.

OverflowException

The number of elements exceeds MaxValue.

The LongCount(Of TSource)(IQueryable(Of TSource)) method generates a MethodCallExpression that represents calling LongCount(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 LongCount(Of TSource)(IQueryable(Of TSource)) depends on the implementation of the type of the source parameter. The expected behavior is that it counts the number of items in source and returns an Int64.

The following code example demonstrates how to use LongCount(Of TSource)(IQueryable(Of TSource)) to count the elements in an array.

        Dim fruits() As String = {"apple", "banana", "mango", _
                              "orange", "passionfruit", "grape"}

        Dim count As Long = fruits.AsQueryable().LongCount()

        MsgBox(String.Format("There are {0} fruits in the collection.", count))

        ' This code produces the following output: 

        ' There are 6 fruits in the collection.

.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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