Queryable.Any 方法

定义

命名空间:

System.Linq

程序集:

System.Linq.Queryable.dll

确定 IQueryable<T> 序列的任何元素是否存在还是满足条件。

重载

Any<TSource>(IQueryable<TSource>)	确定序列是否包含任何元素。
Any<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>)	确定序列的任何元素是否满足条件。

Any<TSource>(IQueryable<TSource>)

Source:

Queryable.cs

确定序列是否包含任何元素。

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

public static bool Any<TSource> (this System.Linq.IQueryable<TSource> source);

static member Any : System.Linq.IQueryable<'Source> -> bool

<Extension()>
Public Function Any(Of TSource) (source As IQueryable(Of TSource)) As Boolean

类型参数

TSource

source的元素的类型。

参数

source

IQueryable<TSource>

要检查是否为空的序列。

返回

Boolean

如果源序列包含任何元素，则 true;否则，false。

例外

ArgumentNullException

source null。

示例

下面的代码示例演示如何使用 Any<TSource>(IQueryable<TSource>) 来确定序列是否包含任何元素。

List<int> numbers = new List<int> { 1, 2 };

// Determine if the list contains any elements.
bool hasElements = numbers.AsQueryable().Any();

Console.WriteLine("The list {0} empty.",
    hasElements ? "is not" : "is");

// This code produces the following output:
//
// The list is not empty.

Dim numbers As New List(Of Integer)(New Integer() {1, 2})

' Determine if the list contains any elements.
Dim hasElements As Boolean = numbers.AsQueryable().Any()

MsgBox(String.Format("The list {0} empty.", _
    IIf(hasElements, "is not", "is")))

' This code produces the following output:
'
' The list is not empty.

Any<TSource>(IQueryable<TSource>) 方法返回的布尔值通常用于 where 子句（Visual Basic 中的Where 子句）的谓词或直接调用 Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) 方法。 以下示例演示如何使用 Any 方法。

class Pet
{
    public string Name { get; set; }
    public int Age { get; set; }
}
class Person
{
    public string LastName { get; set; }
    public Pet[] Pets { get; set; }
}

public static void AnyEx2()
{
    List<Person> people = new List<Person>
        { new Person { LastName = "Haas",
                       Pets = new Pet[] { new Pet { Name="Barley", Age=10 },
                                          new Pet { Name="Boots", Age=14 },
                                          new Pet { Name="Whiskers", Age=6 }}},
          new Person { LastName = "Fakhouri",
                       Pets = new Pet[] { new Pet { Name = "Snowball", Age = 1}}},
          new Person { LastName = "Antebi",
                       Pets = new Pet[] { }},
          new Person { LastName = "Philips",
                       Pets = new Pet[] { new Pet { Name = "Sweetie", Age = 2},
                                          new Pet { Name = "Rover", Age = 13}} }
        };

    // Determine which people have a non-empty Pet array.
    IEnumerable<string> names = from person in people
                                where person.Pets.AsQueryable().Any()
                                select person.LastName;

    foreach (string name in names)
        Console.WriteLine(name);

    /* This code produces the following output:

       Haas
       Fakhouri
       Philips
    */
}

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

Structure Person
    Public LastName As String
    Public Pets() As Pet
End Structure

Sub AnyEx2()
    Dim people As New List(Of Person)(New Person() _
        {New Person With {.LastName = "Haas", _
                          .Pets = New Pet() {New Pet With {.Name = "Barley", .Age = 10}, _
                                             New Pet With {.Name = "Boots", .Age = 14}, _
                                             New Pet With {.Name = "Whiskers", .Age = 6}}}, _
          New Person With {.LastName = "Fakhouri", _
                           .Pets = New Pet() {New Pet With {.Name = "Snowball", .Age = 1}}}, _
          New Person With {.LastName = "Antebi", _
                           .Pets = New Pet() {}}, _
          New Person With {.LastName = "Philips", _
                           .Pets = New Pet() {New Pet With {.Name = "Sweetie", .Age = 2}, _
                                              New Pet With {.Name = "Rover", .Age = 13}}}})

    ' Determine which people have a non-empty Pet array.
    Dim names = From person In people _
                Where person.Pets.AsQueryable().Any() _
                Select person.LastName

    For Each name As String In names
        Console.WriteLine(name)
    Next

    ' This code produces the following output:
    '
    ' Haas
    ' Fakhouri
    ' Philips

End Sub

注解

Any<TSource>(IQueryable<TSource>) 方法生成一个 MethodCallExpression，该 MethodCallExpression 表示调用 Any<TSource>(IQueryable<TSource>) 本身作为构造泛型方法。 然后，它将 MethodCallExpression 传递给由 source 参数 Provider 属性表示的 IQueryProviderExecute<TResult>(Expression) 方法。

由于执行表示调用 Any<TSource>(IQueryable<TSource>) 的表达式树而发生的查询行为取决于 source 参数类型的实现。 预期行为是，它确定 source 是否包含任何元素。

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

Source:

Queryable.cs

确定序列的任何元素是否满足条件。

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

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

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

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

类型参数

TSource

source的元素的类型。

参数

source

IQueryable<TSource>

要测试条件的元素的序列。

predicate

Expression<Func<TSource,Boolean>>

用于测试条件的每个元素的函数。

返回

Boolean

如果源序列中的任何元素都通过指定谓词中的测试，则 true;否则，false。

例外

ArgumentNullException

source 或 predicatenull。

示例

下面的代码示例演示如何使用 Any<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) 来确定序列中的任何元素是否满足条件。

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

public static void AnyEx3()
{
    // Create an array of Pet objects.
    Pet[] pets =
        { new Pet { Name="Barley", Age=8, Vaccinated=true },
          new Pet { Name="Boots", Age=4, Vaccinated=false },
          new Pet { Name="Whiskers", Age=1, Vaccinated=false } };

    // Determine whether any pets over age 1 are also unvaccinated.
    bool unvaccinated =
        pets.AsQueryable().Any(p => p.Age > 1 && p.Vaccinated == false);

    Console.WriteLine(
        "There {0} unvaccinated animals over age one.",
        unvaccinated ? "are" : "are not any");
}

// This code produces the following output:
//
//  There are unvaccinated animals over age one.

Structure Pet
    Dim Name As String
    Dim Age As Integer
    Dim Vaccinated As Boolean
End Structure

Shared Sub AnyEx3()
    ' Create an array of Pet objects.
    Dim pets() As Pet = _
        {New Pet With {.Name = "Barley", .Age = 8, .Vaccinated = True}, _
         New Pet With {.Name = "Boots", .Age = 4, .Vaccinated = False}, _
         New Pet With {.Name = "Whiskers", .Age = 1, .Vaccinated = False}}

    ' Determine whether any pets over age 1 are also unvaccinated.
    Dim unvaccinated As Boolean = _
    pets.AsQueryable().Any(Function(p) p.Age > 1 And p.Vaccinated = False)

    MsgBox(String.Format( _
        "There {0} unvaccinated animals over age one.", _
        IIf(unvaccinated, "are", "are not any") _
    ))
End Sub

' This code produces the following output:
'
'  There are unvaccinated animals over age one.

注解

此方法至少有一个类型参数 Expression<TDelegate> 其类型参数是 Func<T,TResult> 类型之一。 对于这些参数，可以传入 lambda 表达式，并将它编译为 Expression<TDelegate>。

Any<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) 方法生成一个 MethodCallExpression，该 MethodCallExpression 表示调用 Any<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) 本身作为构造泛型方法。 然后，它将 MethodCallExpression 传递给由 source 参数 Provider 属性表示的 IQueryProviderExecute<TResult>(Expression) 方法。

由于执行表示调用 Any<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) 的表达式树而发生的查询行为取决于 source 参数类型的实现。 预期行为是，它确定 source 的任何元素是否满足 predicate指定的条件。