Queryable.ThenByDescending(TSource, TKey) Method (IOrderedQueryable(TSource), Expression(Func(TSource, TKey)), IComparer(TKey))
Performs a subsequent ordering of the elements in a sequence in descending order by using a specified comparer.
Assembly: System.Core (in System.Core.dll)
static member ThenByDescending : source:IOrderedQueryable<'TSource> * keySelector:Expression<Func<'TSource, 'TKey>> * comparer:IComparer<'TKey> -> IOrderedQueryable<'TSource>
The type of the elements of source.
The type of the key that is returned by the keySelector function.
- Type: System.Linq.Expressions.Expression(Func(, ))
A function to extract a key from each element.
Return ValueType: System.Linq.IOrderedQueryable()
A collection whose elements are sorted in descending order according to a key.
Usage NoteIn Visual Basic and C#, you can call this method as an instance method on any object of type IOrderedQueryable(). 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 or comparer 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 ThenBy(TSource, TKey)(IOrderedQueryable(TSource), Expression(Func(TSource, TKey)), IComparer(TKey)) method generates a MethodCallExpression that represents calling ThenBy(TSource, TKey)(IOrderedQueryable(TSource), Expression(Func(TSource, TKey)), IComparer(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)), IComparer(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. The comparer parameter is used to compare key values.