Article
11/18/2011

Queryable.OrderBy<TSource, TKey> Method (IQueryable<TSource>, Expression<Func<TSource, TKey>>)

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Sorts the elements of a sequence in ascending order according to a key.

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

Syntax

'Declaration
<ExtensionAttribute> _
Public Shared Function OrderBy(Of TSource, TKey) ( _
    source As IQueryable(Of TSource), _
    keySelector As Expression(Of Func(Of TSource, TKey)) _
) As IOrderedQueryable(Of TSource)

public static IOrderedQueryable<TSource> OrderBy<TSource, TKey>(
    this IQueryable<TSource> source,
    Expression<Func<TSource, TKey>> keySelector
)

Type Parameters

TSource
The type of the elements of source.

TKey
The type of the key returned by the function that is represented by keySelector.

Parameters

source
Type: System.Linq.IQueryable<TSource>
A sequence of values to order.

keySelector
Type: System.Linq.Expressions.Expression<Func<TSource, TKey>>
A function to extract a key from an element.

Return Value

Type: System.Linq.IOrderedQueryable<TSource>
An IOrderedQueryable<T> whose elements are sorted according to a key.

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 keySelector 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 OrderBy<TSource, TKey>(IQueryable<TSource>, Expression<Func<TSource, TKey>>) method generates a MethodCallExpression that represents calling OrderBy<TSource, TKey>(IQueryable<TSource>, Expression<Func<TSource, TKey>>) itself as a constructed generic method. It then passes the MethodCallExpression to the CreateQuery<TElement>(Expression) method of the IQueryProvider represented by the Provider property of the source parameter. The result of calling CreateQuery<TElement>(Expression) is cast to type IOrderedQueryable<T> and returned.

The query behavior that occurs as a result of executing an expression tree that represents calling OrderBy<TSource, TKey>(IQueryable<TSource>, Expression<Func<TSource, TKey>>) depends on the implementation of the type of the source parameter. The expected behavior is that it sorts the elements of source based on the key obtained by invoking keySelector on each element of source.

Examples

The following code example demonstrates how to use OrderBy<TSource, TKey>(IQueryable<TSource>, Expression<Func<TSource, TKey>>) to sort the elements of a sequence.

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

   Shared Sub OrderByEx1()
      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}}

      ' Sort the Pet objects in the array by Pet.Age.
      Dim query As IEnumerable(Of Pet) = _
                  pets.AsQueryable().OrderBy(Function(pet) pet.Age)

      Dim output As New System.Text.StringBuilder
      For Each pet As Pet In query
         output.AppendLine(String.Format("{0} - {1}", pet.Name, pet.Age))
      Next

      ' Display the output.
      outputBlock.Text &= output.ToString() & vbCrLf
   End Sub

   ' This code produces the following output:

   ' Whiskers - 1
   ' Boots - 4
   ' Barley - 8

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

         public static void OrderByEx1()
         {
            Pet[] pets = { new Pet { Name="Barley", Age=8 },
                               new Pet { Name="Boots", Age=4 },
                               new Pet { Name="Whiskers", Age=1 } };

            // Sort the Pet objects in the array by Pet.Age.
            IEnumerable<Pet> query =
                pets.AsQueryable().OrderBy(pet => pet.Age);

            foreach (Pet pet in query)
               outputBlock.Text += String.Format("{0} - {1}", pet.Name, pet.Age) + "\n";
         }

         /*
             This code produces the following output:

             Whiskers - 1
             Boots - 4
             Barley - 8
         */

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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