• Article

Queryable.SelectMany<TSource, TCollection, TResult> Method (IQueryable<TSource>, Expression<Func<TSource, Int32, IEnumerable<TCollection>>>, Expression<Func<TSource, TCollection, TResult>>)

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Projects each element of a sequence to an IEnumerable<T> that incorporates the index of the source element that produced it. A result selector function is invoked on each element of each intermediate sequence, and the resulting values are combined into a single, one-dimensional sequence and returned.

Namespace:  System.Linq
Assembly:  System.Core (in System.Core.dll)

Syntax

'Declaration
<ExtensionAttribute> _
Public Shared Function SelectMany(Of TSource, TCollection, TResult) ( _
    source As IQueryable(Of TSource), _
    collectionSelector As Expression(Of Func(Of TSource, Integer, IEnumerable(Of TCollection))), _
    resultSelector As Expression(Of Func(Of TSource, TCollection, TResult)) _
) As IQueryable(Of TResult)

public static IQueryable<TResult> SelectMany<TSource, TCollection, TResult>(
    this IQueryable<TSource> source,
    Expression<Func<TSource, int, IEnumerable<TCollection>>> collectionSelector,
    Expression<Func<TSource, TCollection, TResult>> resultSelector
)

Type Parameters

  • TSource
    The type of the elements of source.
  • TCollection
    The type of the intermediate elements collected by the function represented by collectionSelector.
  • TResult
    The type of the elements of the resulting sequence.

Parameters

Return Value

Type: System.Linq.IQueryable<TResult>
An IQueryable<T> whose elements are the result of invoking the one-to-many projection function collectionSelector on each element of source and then mapping each of those sequence elements and their corresponding source element to a result element.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IQueryable<TSource>. When you use instance method syntax to call this method, omit the first parameter.

Exceptions

Exception Condition
ArgumentNullException

source or collectionSelector or resultSelector 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 SelectMany<TSource, TCollection, TResult>(IQueryable<TSource>, Expression<Func<TSource, Int32, IEnumerable<TCollection>>>, Expression<Func<TSource, TCollection, TResult>>) method generates a MethodCallExpression that represents calling SelectMany<TSource, TCollection, TResult>(IQueryable<TSource>, Expression<Func<TSource, Int32, IEnumerable<TCollection>>>, Expression<Func<TSource, TCollection, TResult>>) itself as a constructed generic method. It then passes the MethodCallExpression to the CreateQuery(Expression) method of the IQueryProvider represented by the Provider property of the source parameter.

The query behavior that occurs as a result of executing an expression tree that represents calling SelectMany<TSource, TCollection, TResult>(IQueryable<TSource>, Expression<Func<TSource, Int32, IEnumerable<TCollection>>>, Expression<Func<TSource, TCollection, TResult>>) depends on the implementation of the type of the source parameter. The expected behavior is that it invokes collectionSelector on each element of source to project it into an enumerable form. Each enumerable result incorporates the source element's index. Then the function represented by resultSelector is invoked on each element in each intermediate sequence. The resulting values are concatenated into a single, one-dimensional sequence.

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.