Queryable.Max 方法

定义

重载

Max<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,TResult>>)

对泛型 IQueryable<T> 的每个元素调用投影函数,并返回最大结果值。Invokes a projection function on each element of a generic IQueryable<T> and returns the maximum resulting value.

Max<TSource>(IQueryable<TSource>)

返回泛型 IQueryable<T> 中的最大值。Returns the maximum value in a generic IQueryable<T>.

Max<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,TResult>>)

对泛型 IQueryable<T> 的每个元素调用投影函数,并返回最大结果值。Invokes a projection function on each element of a generic IQueryable<T> and returns the maximum resulting value.

public:
generic <typename TSource, typename TResult>
[System::Runtime::CompilerServices::Extension]
 static TResult Max(System::Linq::IQueryable<TSource> ^ source, System::Linq::Expressions::Expression<Func<TSource, TResult> ^> ^ selector);
public static TResult Max<TSource,TResult> (this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<Func<TSource,TResult>> selector);
static member Max : System.Linq.IQueryable<'Source> * System.Linq.Expressions.Expression<Func<'Source, 'Result>> -> 'Result
<Extension()>
Public Function Max(Of TSource, TResult) (source As IQueryable(Of TSource), selector As Expression(Of Func(Of TSource, TResult))) As TResult

类型参数

TSource

source 的元素类型。The type of the elements of source.

TResult

selector 表示的函数返回的值类型。The type of the value returned by the function represented by selector.

参数

source
IQueryable<TSource>

要确定最大值的值序列。A sequence of values to determine the maximum of.

selector
Expression<Func<TSource,TResult>>

要应用于每个元素的投影函数。A projection function to apply to each element.

返回

TResult

序列中的最大值。The maximum value in the sequence.

异常

sourceselectornullsource or selector is null.

示例

下面的代码示例演示如何使用 Max<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,TResult>>) 来确定投影值序列中的最大值。The following code example demonstrates how to use Max<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,TResult>>) to determine the maximum value in a sequence of projected values.

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

public static void MaxEx2()
{
    Pet[] pets = { new Pet { Name="Barley", Age=8 },
                   new Pet { Name="Boots", Age=4 },
                   new Pet { Name="Whiskers", Age=1 } };

    // Add Pet.Age to the length of Pet.Name
    // to determine the "maximum" Pet object in the array.
    int max =
        pets.AsQueryable().Max(pet => pet.Age + pet.Name.Length);

    Console.WriteLine(
        "The maximum pet age plus name length is {0}.",
        max);
}

/*
    This code produces the following output:

    The maximum pet age plus name length is 14.
*/

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

Shared Sub MaxEx2()
    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}}

    ' Add Pet.Age to the length of Pet.Name
    ' to determine the "maximum" Pet object in the array.
    Dim max As Integer = _
        pets.AsQueryable().Max(Function(pet) pet.Age + pet.Name.Length)

    MsgBox(String.Format("The maximum pet age plus name length is {0}.", max))

    'This code produces the following output:

    'The maximum pet age plus name length is 14.

注解

此方法至少具有一个类型 Expression<TDelegate> 的参数,其类型参数为 Func<T,TResult> 类型之一。This method has at least one parameter of type Expression<TDelegate> whose type argument is one of the Func<T,TResult> types. 对于这些参数,可以传入 lambda 表达式,并将其编译为 Expression<TDelegate>For these parameters, you can pass in a lambda expression and it will be compiled to an Expression<TDelegate>.

Max<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,TResult>>) 方法生成一个 MethodCallExpression,它表示作为构造的泛型方法调用 Max<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,TResult>>) 本身。The Max<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,TResult>>) method generates a MethodCallExpression that represents calling Max<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,TResult>>) itself as a constructed generic method. 然后,它将 MethodCallExpression 传递到 IQueryProviderExecute<TResult>(Expression) 方法(由 source 参数的 Provider 属性表示)。It then passes the MethodCallExpression to the Execute<TResult>(Expression) method of the IQueryProvider represented by the Provider property of the source parameter.

因执行表示调用 Max<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,TResult>>) 的表达式树而发生的查询行为取决于 source 参数类型的实现。The query behavior that occurs as a result of executing an expression tree that represents calling Max<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,TResult>>) depends on the implementation of the type of the source parameter. 预期的行为是,它在 source 中的每个元素上调用 selector,并返回最大值。The expected behavior is that it invokes selector on each element in source and returns the maximum value.

Max<TSource>(IQueryable<TSource>)

返回泛型 IQueryable<T> 中的最大值。Returns the maximum value in a generic IQueryable<T>.

public:
generic <typename TSource>
[System::Runtime::CompilerServices::Extension]
 static TSource Max(System::Linq::IQueryable<TSource> ^ source);
public static TSource Max<TSource> (this System.Linq.IQueryable<TSource> source);
static member Max : System.Linq.IQueryable<'Source> -> 'Source
<Extension()>
Public Function Max(Of TSource) (source As IQueryable(Of TSource)) As TSource

类型参数

TSource

source 的元素类型。The type of the elements of source.

参数

source
IQueryable<TSource>

要确定最大值的值序列。A sequence of values to determine the maximum of.

返回

TSource

序列中的最大值。The maximum value in the sequence.

异常

sourcenullsource is null.

示例

下面的代码示例演示如何使用 Max<TSource>(IQueryable<TSource>) 来确定序列中的最大值。The following code example demonstrates how to use Max<TSource>(IQueryable<TSource>) to determine the maximum value in a sequence.

List<long> longs = new List<long> { 4294967296L, 466855135L, 81125L };

long max = longs.AsQueryable().Max();

Console.WriteLine("The largest number is {0}.", max);

/*
    This code produces the following output:

    The largest number is 4294967296.
*/

Dim longs As New List(Of Long)(New Long() {4294967296L, 466855135L, 81125L})

Dim max As Long = longs.AsQueryable().Max()

MsgBox(String.Format("The largest number is {0}.", max))

'This code produces the following output:

'The largest number is 4294967296.

注解

Max<TSource>(IQueryable<TSource>) 方法生成一个 MethodCallExpression,它表示作为构造的泛型方法调用 Max<TSource>(IQueryable<TSource>) 本身。The Max<TSource>(IQueryable<TSource>) method generates a MethodCallExpression that represents calling Max<TSource>(IQueryable<TSource>) itself as a constructed generic method. 然后,它将 MethodCallExpression 传递到 IQueryProviderExecute<TResult>(Expression) 方法(由 source 参数的 Provider 属性表示)。It then passes the MethodCallExpression to the Execute<TResult>(Expression) method of the IQueryProvider represented by the Provider property of the source parameter.

因执行表示调用 Max<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。The query behavior that occurs as a result of executing an expression tree that represents calling Max<TSource>(IQueryable<TSource>) depends on the implementation of the type of the source parameter. 预期的行为是返回 source中的最大值。The expected behavior is that it returns the maximum value in source.

适用于