Queryable.All<TSource> 方法

定义

命名空间:

System.Linq

程序集:

System.Linq.Queryable.dll

程序集:

System.Core.dll

程序集:

netstandard.dll

确定序列中的所有元素是否都满足条件。

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

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

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

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

类型参数

TSource

source 的元素类型。

参数

source

IQueryable<TSource>

要测试其元素是否满足条件的序列。

predicate

Expression<Func<TSource,Boolean>>

用于测试每个元素是否满足条件的函数。

返回

Boolean

如果源序列中的每个元素都通过指定谓词中的测试，或者序列为空，则为 true；否则为 false。

例外

ArgumentNullException

source 或 predicate 为 null。

示例

下面的代码示例演示如何用于 All<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) 确定序列中的所有元素是否满足条件。

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

public static void AllEx1()
{
    // Create an array of Pets.
    Pet[] pets = { new Pet { Name="Barley", Age=10 },
                   new Pet { Name="Boots", Age=4 },
                   new Pet { Name="Whiskers", Age=6 } };

    // Determine whether all pet names in the array start with 'B'.
    bool allStartWithB =
        pets.AsQueryable().All(pet => pet.Name.StartsWith("B"));

    Console.WriteLine(
        "{0} pet names start with 'B'.",
        allStartWithB ? "All" : "Not all");
}

// This code produces the following output:
//
//  Not all pet names start with 'B'.

Sub AllEx()
    ' Create an array of Pets.
    Dim pets() As Pet = _
        {New Pet With {.Name = "Barley", .Age = 10}, _
         New Pet With {.Name = "Boots", .Age = 4}, _
         New Pet With {.Name = "Whiskers", .Age = 6}}

    ' Determine whether all pet names in the array start with 'B'.
    Dim allStartWithB As Boolean = _
        pets.AsQueryable().All(Function(ByVal pet) pet.Name.StartsWith("B"))

    MsgBox(String.Format( _
        "{0} pet names start with 'B'.", _
        IIf(allStartWithB, "All", "Not all")))
End Sub

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

' This code produces the following output:
'
'  Not all pet names start with 'B'.

方法返回的布尔值All<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>)通常用于 Visual Basic) 中的子句 (Where子句的谓where词或直接调用Where方法。 以下示例演示了此方法的 All 这种用法。

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 AllEx2()
{
    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 Pet { Name = "Belle", Age = 8} }},
          new Person { LastName = "Philips",
                       Pets = new Pet[] { new Pet { Name = "Sweetie", Age = 2},
                                          new Pet { Name = "Rover", Age = 13}} }
        };

    // Determine which people have pets that are all older than 5.
    IEnumerable<string> names = from person in people
                                where person.Pets.AsQueryable().All(pet => pet.Age > 5)
                                select person.LastName;

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

    /* This code produces the following output:
     *
     * Haas
     * Antebi
     */
}

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 AllEx2()
    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 Pet With {.Name = "Belle", .Age = 8}}}, _
          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 pets that are all older than 5.
    Dim names = From person In people _
                Where person.Pets.AsQueryable().All(Function(pet) pet.Age > 5) _
                Select person.LastName

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

    ' This code produces the following output:
    '
    ' Haas
    ' Antebi

End Sub

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All<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>)生成一个表示自己作为构造泛型方法调用All<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>)自身的方法MethodCallExpression。 然后，MethodCallExpressionExecute<TResult>(Expression)它将传递给由参数属性source表示Provider的方法IQueryProvider。

执行表示调用 All<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实现 source 。 预期行为是，它确定是否满足条件predicate中的所有元素source。