Статья
11/18/2011

Queryable.Max<TSource, TResult> Method (IQueryable<TSource>, Expression<Func<TSource, TResult>>)

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Invokes a projection function on each element of a generic IQueryable<T> and returns the maximum resulting value.

Namespace: System.Linq
Assembly: System.Core (in System.Core.dll)

Syntax

'Declaration
<ExtensionAttribute> _
Public Shared Function Max(Of TSource, TResult) ( _
    source As IQueryable(Of TSource), _
    selector As Expression(Of Func(Of TSource, TResult)) _
) As TResult

public static TResult Max<TSource, TResult>(
    this IQueryable<TSource> source,
    Expression<Func<TSource, TResult>> selector
)

Type Parameters

TSource
The type of the elements of source.

TResult
The type of the value returned by the function represented by selector.

Parameters

source
Type: System.Linq.IQueryable<TSource>
A sequence of values to determine the maximum of.

selector
Type: System.Linq.Expressions.Expression<Func<TSource, TResult>>
A projection function to apply to each element.

Return Value

Type: TResult
The maximum value in the sequence.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IQueryable<TSource>. When you use instance method syntax to call this method, omit the first parameter.

Exceptions

Exception	Condition
ArgumentNullException	source or selector is nulla null reference (Nothing in Visual Basic).

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 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. 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 Max<TSource, TResult>(IQueryable<TSource>, Expression<Func<TSource, TResult>>) depends on the implementation of the type of the source parameter. The expected behavior is that it invokes selector on each element in source and returns the maximum value.

Examples

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.

   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)

      outputBlock.Text &= String.Format("The maximum pet age plus name length is {0}.", max) & vbCrLf

      'This code produces the following output:

      'The maximum pet age plus name length is 14.

         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);

            outputBlock.Text += String.Format(
                "The maximum pet age plus name length is {0}.",
                max) + "\n";
         }

         /*
             This code produces the following output:

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

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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