Articolo
11/18/2011

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

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

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

Syntax

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

public static long LongCount<TSource>(
    this IQueryable<TSource> source
)

Type Parameters

TSource
The type of the elements of source.

Parameters

source
Type: System.Linq.IQueryable<TSource>
An IQueryable<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<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).
OverflowException	The number of elements exceeds MaxValue.

Remarks

The LongCount<TSource>(IQueryable<TSource>) method generates a MethodCallExpression that represents calling LongCount<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 LongCount<TSource>(IQueryable<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.

Examples

The following code example demonstrates how to use LongCount<TSource>(IQueryable<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()

      outputBlock.Text &= String.Format("There are {0} fruits in the collection.", count) & vbCrLf

      ' This code produces the following output:

      ' There are 6 fruits in the collection.

         string[] fruits = { "apple", "banana", "mango", 
                                  "orange", "passionfruit", "grape" };

         long count = fruits.AsQueryable().LongCount();

         outputBlock.Text += String.Format("There are {0} fruits in the collection.", count) + "\n";

         /*
             This code produces the following output:

             There are 6 fruits in the collection.
         */

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.

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