Queryable.Count 方法

Source:

Queryable.cs

Source:

Queryable.cs

Source:

Queryable.cs

Source:

Queryable.cs

Source:

Queryable.cs

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);

[System.Diagnostics.CodeAnalysis.RequiresDynamicCode("Enumerating collections as IQueryable can require creating new generic types or methods, which requires creating code at runtime. This may not work when AOT compiling.")]
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

[<System.Diagnostics.CodeAnalysis.RequiresDynamicCode("Enumerating collections as IQueryable can require creating new generic types or methods, which requires creating code at runtime. This may not work when AOT compiling.")>]
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

类型参数

参数

返回

序列中满足谓词函数中条件的元素数。

属性

RequiresDynamicCodeAttribute

例外

示例

下面的代码示例演示如何用于 Count<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) 对满足条件的序列中的元素进行计数。

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);

    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.

注解

此方法至少有一个类型 Expression<TDelegate> 参数，其类型参数为类型之 Func<T,TResult> 一。 对于这些参数，可以传入 lambda 表达式，并将它编译为一个 Expression<TDelegate>。

该方法Count<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>)生成一个表示调用Count<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>)自身为已构造泛型方法的一MethodCallExpression个方法。 然后，它将传递给MethodCallExpressionExecute<TResult>(Expression)由参数属性source表示Provider的方法IQueryProvider。

执行表示调用 Count<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) 的表达式树导致的查询行为取决于参数类型的 source 实现。 预期行为是，它计算满足指定predicate条件的项source数。

Source:

Queryable.cs

Source:

Queryable.cs

Source:

Queryable.cs

Source:

Queryable.cs

Source:

Queryable.cs

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);

[System.Diagnostics.CodeAnalysis.RequiresDynamicCode("Enumerating collections as IQueryable can require creating new generic types or methods, which requires creating code at runtime. This may not work when AOT compiling.")]
public static int Count<TSource>(this System.Linq.IQueryable<TSource> source);

static member Count : System.Linq.IQueryable<'Source> -> int

[<System.Diagnostics.CodeAnalysis.RequiresDynamicCode("Enumerating collections as IQueryable can require creating new generic types or methods, which requires creating code at runtime. This may not work when AOT compiling.")>]
static member Count : System.Linq.IQueryable<'Source> -> int

<Extension()>
Public Function Count(Of TSource) (source As IQueryable(Of TSource)) As Integer

类型参数

参数

返回

输入序列中的元素数。

属性

RequiresDynamicCodeAttribute

例外

示例

下面的代码示例演示如何用于 Count<TSource>(IQueryable<TSource>) 对序列中的元素进行计数。

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.

注解

该方法Count<TSource>(IQueryable<TSource>)生成一个表示调用Count<TSource>(IQueryable<TSource>)自身为已构造泛型方法的一MethodCallExpression个方法。 然后，它将传递给MethodCallExpressionExecute<TResult>(Expression)由参数属性source表示Provider的方法IQueryProvider。

执行表示调用 Count<TSource>(IQueryable<TSource>) 的表达式树导致的查询行为取决于参数类型的 source 实现。 预期行为是它计算项 source的数目。