Queryable.ThenByDescending<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 descending order, according to a key.
Namespace: System.Linq
Assembly: System.Core (in System.Core.dll)
Syntax
'Declaration
<ExtensionAttribute> _
Public Shared Function ThenByDescending(Of TSource, TKey) ( _
source As IOrderedQueryable(Of TSource), _
keySelector As Expression(Of Func(Of TSource, TKey)) _
) As IOrderedQueryable(Of TSource)
public static IOrderedQueryable<TSource> ThenByDescending<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 in descending order 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 ThenByDescending<TSource, TKey>(IOrderedQueryable<TSource>, Expression<Func<TSource, TKey>>) method generates a MethodCallExpression that represents calling ThenByDescending<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 ThenByDescending<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 in descending order, based on the key obtained by invoking keySelector on each element of source. All previously established sort orders are preserved.
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.