Queryable.Count Method
Definition
Important
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Returns the number of elements in a sequence.
Overloads
Count<TSource>(IQueryable<TSource>) |
Returns the number of elements in a sequence. |
Count<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) |
Returns the number of elements in the specified sequence that satisfies a condition. |
Count<TSource>(IQueryable<TSource>)
- Source:
- Queryable.cs
- Source:
- Queryable.cs
- Source:
- Queryable.cs
Returns the number of elements in a sequence.
public:
generic <typename TSource>
[System::Runtime::CompilerServices::Extension]
static int Count(System::Linq::IQueryable<TSource> ^ source);
public static int Count<TSource> (this System.Linq.IQueryable<TSource> source);
static member Count : System.Linq.IQueryable<'Source> -> int
<Extension()>
Public Function Count(Of TSource) (source As IQueryable(Of TSource)) As Integer
Type Parameters
- TSource
The type of the elements of source
.
Parameters
- source
- IQueryable<TSource>
The IQueryable<T> that contains the elements to be counted.
Returns
The number of elements in the input sequence.
Exceptions
source
is null
.
The number of elements in source
is larger than Int32.MaxValue.
Examples
The following code example demonstrates how to use Count<TSource>(IQueryable<TSource>) to count the elements in a sequence.
string[] fruits = { "apple", "banana", "mango",
"orange", "passionfruit", "grape" };
int numberOfFruits = fruits.AsQueryable().Count();
Console.WriteLine(
"There are {0} items in the array.",
numberOfFruits);
// This code produces the following output:
//
// There are 6 items in the array.
Dim fruits() As String = {"apple", "banana", "mango", _
"orange", "passionfruit", "grape"}
Dim numberOfFruits As Integer = fruits.AsQueryable().Count()
MsgBox(String.Format( _
"There are {0} items in the array.", _
numberOfFruits))
' This code produces the following output:
'
' There are 6 items in the array.
Remarks
The Count<TSource>(IQueryable<TSource>) method generates a MethodCallExpression that represents calling Count<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 Count<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
.
Applies to
Count<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>)
- Source:
- Queryable.cs
- Source:
- Queryable.cs
- Source:
- Queryable.cs
Returns the number of elements in the specified sequence that satisfies a condition.
public:
generic <typename TSource>
[System::Runtime::CompilerServices::Extension]
static int Count(System::Linq::IQueryable<TSource> ^ source, System::Linq::Expressions::Expression<Func<TSource, bool> ^> ^ predicate);
public static int Count<TSource> (this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<Func<TSource,bool>> predicate);
static member Count : System.Linq.IQueryable<'Source> * System.Linq.Expressions.Expression<Func<'Source, bool>> -> int
<Extension()>
Public Function Count(Of TSource) (source As IQueryable(Of TSource), predicate As Expression(Of Func(Of TSource, Boolean))) As Integer
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
The number of elements in the sequence that satisfies the condition in the predicate function.
Exceptions
source
or predicate
is null
.
The number of elements in source
is larger than Int32.MaxValue.
Examples
The following code example demonstrates how to use Count<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) to count the elements in a sequence that satisfy a condition.
class Pet
{
public string Name { get; set; }
public bool Vaccinated { get; set; }
}
public static void CountEx2()
{
// Create an array of Pet objects.
Pet[] pets = { new Pet { Name="Barley", Vaccinated=true },
new Pet { Name="Boots", Vaccinated=false },
new Pet { Name="Whiskers", Vaccinated=false } };
// Count the number of unvaccinated pets in the array.
int numberUnvaccinated =
pets.AsQueryable().Count(p => p.Vaccinated == false);
Console.WriteLine(
"There are {0} unvaccinated animals.",
numberUnvaccinated);
}
// This code produces the following output:
//
// There are 2 unvaccinated animals.
Structure Pet
Public Name As String
Public Vaccinated As Boolean
End Structure
Shared Sub CountEx2()
' Create an array of Pet objects.
Dim pets() As Pet = {New Pet With {.Name = "Barley", .Vaccinated = True}, _
New Pet With {.Name = "Boots", .Vaccinated = False}, _
New Pet With {.Name = "Whiskers", .Vaccinated = False}}
' Count the number of unvaccinated pets in the array.
Dim numberUnvaccinated As Integer = pets.AsQueryable().Count(Function(p) p.Vaccinated = False)
MsgBox(String.Format("There are {0} unvaccinated animals.", numberUnvaccinated))
End Sub
' This code produces the following output:
'
' There are 2 unvaccinated animals.
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 Count<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) method generates a MethodCallExpression that represents calling Count<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 Count<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
.
Applies to
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