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

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)

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

source
Type: System.Linq.IQueryable<TSource>

A sequence of values to project.

collectionSelector
Type: System.Linq.Expressions.Expression<Func<TSource, Int32, IEnumerable<TCollection>>>

A projection function to apply to each element of the input sequence; the second parameter of this function represents the index of the source element.

resultSelector
Type: System.Linq.Expressions.Expression<Func<TSource, TCollection, TResult>>

A projection function to apply to each element of each intermediate sequence.

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. For more information, see Extension Methods (Visual Basic) or Extension Methods (C# Programming Guide).

ExceptionCondition
ArgumentNullException

source or collectionSelector or resultSelector 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 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.

Windows 7, Windows Vista, Windows XP SP2, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003

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

.NET Framework

Supported in: 3.5

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