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Queryable.ThenByDescending(TSource, TKey) Method (IOrderedQueryable(TSource), Expression(Func(TSource, TKey)))

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)

static member ThenByDescending : 
        source:IOrderedQueryable<'TSource> * 
        keySelector:Expression<Func<'TSource, 'TKey>> -> IOrderedQueryable<'TSource> 

Type Parameters


The type of the elements of source.


The type of the key returned by the function represented by keySelector.


Type: System.Linq.IOrderedQueryable(TSource)
An IOrderedQueryable(T) that contains elements to sort.
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. For more information, see Extension Methods (Visual Basic) or Extension Methods (C# Programming Guide).


source or keySelector is a null reference (Nothing in Visual Basic).

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.

.NET Framework

Supported in: 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.