Artikel
11/18/2011

Queryable.ThenBy<TSource, TKey> Method (IOrderedQueryable<TSource>, Expression<Func<TSource, TKey>>)

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Performs a subsequent ordering of the elements in 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 ThenBy(Of TSource, TKey) ( _
    source As IOrderedQueryable(Of TSource), _
    keySelector As Expression(Of Func(Of TSource, TKey)) _
) As IOrderedQueryable(Of TSource)

public static IOrderedQueryable<TSource> ThenBy<TSource, TKey>(
    this IOrderedQueryable<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 represented by keySelector.

Parameters

source
Type: System.Linq.IOrderedQueryable<TSource>
An IOrderedQueryable<T> that contains elements to sort.

keySelector
Type: System.Linq.Expressions.Expression<Func<TSource, TKey>>
A function to extract a key from each 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 IOrderedQueryable<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 ThenBy<TSource, TKey>(IOrderedQueryable<TSource>, Expression<Func<TSource, TKey>>) method generates a MethodCallExpression that represents calling ThenBy<TSource, TKey>(IOrderedQueryable<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 ThenBy<TSource, TKey>(IOrderedQueryable<TSource>, Expression<Func<TSource, TKey>>) depends on the implementation of the type of the source parameter. The expected behavior is that it performs a secondary sort of the elements of source based on the key obtained by invoking keySelector on each element of source. All previously established sort orders are preserved.

Examples

The following code example demonstrates how to use ThenBy<TSource, TKey>(IOrderedQueryable<TSource>, Expression<Func<TSource, TKey>>) to perform a secondary ordering of the elements in a sequence.

      Dim fruits() As String = _
          {"grape", "passionfruit", "banana", "mango", _
           "orange", "raspberry", "apple", "blueberry"}

      ' Sort the strings first by their length and then 
      ' alphabetically by passing the identity selector function.
      Dim query = fruits.AsQueryable() _
          .OrderBy(Function(fruit) fruit.Length).ThenBy(Function(fruit) fruit)

      ' Display the results.
      Dim output As New System.Text.StringBuilder
      For Each fruit As String In query
         output.AppendLine(fruit)
      Next
      outputBlock.Text &= output.ToString() & vbCrLf

      'This code produces the following output:

      'apple
      'grape
      'mango
      'banana
      'orange
      'blueberry
      'raspberry
      'passionfruit

         string[] fruits = { "grape", "passionfruit", "banana", "apple", 
                                  "orange", "raspberry", "mango", "blueberry" };

         // Sort the strings first by their length and then 
         // alphabetically by passing the identity selector function.
         IEnumerable<string> query =
             fruits.AsQueryable()
             .OrderBy(fruit => fruit.Length).ThenBy(fruit => fruit);

         foreach (string fruit in query)
            outputBlock.Text += fruit + "\n";

         /*
             This code produces the following output:

             apple
             grape
             mango
             banana
             orange
             blueberry
             raspberry
             passionfruit
         */

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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