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


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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)

Public Shared Function ThenBy(Of TSource, TKey) (
	source As IOrderedQueryable(Of TSource),
	keySelector As Expression(Of Func(Of TSource, TKey))
) As IOrderedQueryable(Of TSource)


Type: System.Linq.IOrderedQueryable(Of TSource)

An IOrderedQueryable(Of T) that contains elements to sort.

Type: System.Linq.Expressions.Expression(Of Func(Of TSource, TKey))

A function to extract a key from each element.

Return Value

Type: System.Linq.IOrderedQueryable(Of TSource)

An IOrderedQueryable(Of T) whose elements are sorted according to a key.

Type Parameters


The type of the elements of source.


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

Exception Condition

source or keySelector is null.

This method has at least one parameter of type Expression(Of TDelegate) whose type argument is one of the Func(Of T, TResult) types. For these parameters, you can pass in a lambda expression and it will be compiled to an Expression(Of TDelegate).

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

The query behavior that occurs as a result of executing an expression tree that represents calling ThenBy(Of TSource, TKey)(IOrderedQueryable(Of TSource), Expression(Of Func(Of 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.

The following code example demonstrates how to use ThenBy(Of TSource, TKey)(IOrderedQueryable(Of TSource), Expression(Of Func(Of 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

'This code produces the following output:


Universal Windows Platform
Available since 8
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.1
Windows Phone
Available since 8.1
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