Queryable.ThenBy<TSource, TKey> Method (IOrderedQueryable<TSource>, Expression<Func<TSource, TKey>>)
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 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. For more information, see Extension Methods (Visual Basic) or Extension Methods (C# Programming Guide).| Exception | Condition |
|---|---|
| ArgumentNullException | source or keySelector is null. |
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.
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.
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)
Console.WriteLine(fruit);
/*
This code produces the following output:
apple
grape
mango
banana
orange
blueberry
raspberry
passionfruit
*/
Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
