Queryable.LongCount Method

Definition

Namespace:

System.Linq

Assembly:

System.Linq.Queryable.dll

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

Overloads

LongCount<TSource>(IQueryable<TSource>)	Returns an Int64 that represents the total number of elements in a sequence.
LongCount<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>)	Returns an Int64 that represents the number of elements in a sequence that satisfy a condition.

LongCount<TSource>(IQueryable<TSource>)

Source:

Queryable.cs

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

public:
generic <typename TSource>
[System::Runtime::CompilerServices::Extension]
 static long LongCount(System::Linq::IQueryable<TSource> ^ source);

public static long LongCount<TSource> (this System.Linq.IQueryable<TSource> source);

static member LongCount : System.Linq.IQueryable<'Source> -> int64

<Extension()>
Public Function LongCount(Of TSource) (source As IQueryable(Of TSource)) As Long

Type Parameters

TSource

The type of the elements of source.

Parameters

source

IQueryable<TSource>

An IQueryable<T> that contains the elements to be counted.

Returns

Int64

The number of elements in source.

Exceptions

ArgumentNullException

source is null.

OverflowException

The number of elements exceeds Int64.MaxValue.

Examples

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

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

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

Console.WriteLine("There are {0} fruits in the collection.", count);

/*
    This code produces the following output:

    There are 6 fruits in the collection.
*/

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.

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.

LongCount<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>)

Source:

Queryable.cs

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

public:
generic <typename TSource>
[System::Runtime::CompilerServices::Extension]
 static long LongCount(System::Linq::IQueryable<TSource> ^ source, System::Linq::Expressions::Expression<Func<TSource, bool> ^> ^ predicate);

public static long LongCount<TSource> (this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<Func<TSource,bool>> predicate);

static member LongCount : System.Linq.IQueryable<'Source> * System.Linq.Expressions.Expression<Func<'Source, bool>> -> int64

<Extension()>
Public Function LongCount(Of TSource) (source As IQueryable(Of TSource), predicate As Expression(Of Func(Of TSource, Boolean))) As Long

Type Parameters

TSource

The type of the elements of source.

Parameters

source

IQueryable<TSource>

An IQueryable<T> that contains the elements to be counted.

predicate

Expression<Func<TSource,Boolean>>

A function to test each element for a condition.

Returns

Int64

The number of elements in source that satisfy the condition in the predicate function.

Exceptions

ArgumentNullException

source or predicate is null.

OverflowException

The number of matching elements exceeds Int64.MaxValue.

Examples

The following code example demonstrates how to use LongCount<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) to count the elements in an array that satisfy a condition.

class Pet
{
    public string Name { get; set; }
    public int Age { get; set; }
}

public static void LongCountEx2()
{
    Pet[] pets = { new Pet { Name="Barley", Age=8 },
                   new Pet { Name="Boots", Age=4 },
                   new Pet { Name="Whiskers", Age=1 } };

    const int Age = 3;

    // Count the number of Pet objects where Pet.Age is greater than 3.
    long count = pets.AsQueryable().LongCount(pet => pet.Age > Age);

    Console.WriteLine("There are {0} animals over age {1}.", count, Age);
}

/*
    This code produces the following output:

    There are 2 animals over age 3.
*/

Structure Pet
    Public Name As String
    Public Age As Integer
End Structure

Shared Sub LongCountEx2()
    Dim pets() As Pet = {New Pet With {.Name = "Barley", .Age = 8}, _
                       New Pet With {.Name = "Boots", .Age = 4}, _
                       New Pet With {.Name = "Whiskers", .Age = 1}}

    Const Age As Integer = 3

    ' Count the number of Pet objects where Pet.Age is greater than 3.
    Dim count As Long = pets.AsQueryable().LongCount(Function(Pet) Pet.Age > Age)

    MsgBox(String.Format("There are {0} animals over age {1}.", count, Age))
End Sub

' This code produces the following output:

' There are 2 animals over age 3.

Remarks

This method has at least one parameter of type Expression<TDelegate> whose type argument is one of the Func<T,TResult> types. For these parameters, you can pass in a lambda expression and it will be compiled to an Expression<TDelegate>.

The LongCount<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) method generates a MethodCallExpression that represents calling LongCount<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) 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>, Expression<Func<TSource,Boolean>>) depends on the implementation of the type of the source parameter. The expected behavior is that it counts the number of items in source that satisfy the condition specified by predicate and returns an Int64.