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.
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 )
The type of the elements of source.
The type of the intermediate elements collected by the function represented by collectionSelector.
The type of the elements of the resulting sequence.
- Type: System.Linq.IQueryable<>
A sequence of values to project.
- Type: System.Linq.Expressions.Expression<Func<, Int32, IEnumerable<>>>
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.
Return ValueType: System.Linq.IQueryable<>
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 NoteIn Visual Basic and C#, you can call this method as an instance method on any object of type IQueryable<>. 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 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 method generates a MethodCallExpression that represents calling 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 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.