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

Projects each element of a sequence to an IEnumerable<T> and combines the resulting sequences into one sequence. The index of each source element is used in the projected form of that element.

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

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

Type Parameters

TSource

The type of the elements of source.

TResult

The type of the elements of the sequence returned by the function represented by selector.

Parameters

source
Type: System.Linq.IQueryable<TSource>
A sequence of values to project.
selector
Type: System.Linq.Expressions.Expression<Func<TSource, Int32, IEnumerable<TResult>>>
A projection function to apply to each element; the second parameter of this function represents the index of the source element.

Return Value

Type: System.Linq.IQueryable<TResult>
An IQueryable<T> whose elements are the result of invoking a one-to-many projection function on each element of the input sequence.

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.

ExceptionCondition
ArgumentNullException

source or selector 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, TResult>(IQueryable<TSource>, Expression<Func<TSource, Int32, IEnumerable<TResult>>>) method generates a MethodCallExpression that represents calling SelectMany<TSource, TResult>(IQueryable<TSource>, Expression<Func<TSource, Int32, IEnumerable<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, TResult>(IQueryable<TSource>, Expression<Func<TSource, Int32, IEnumerable<TResult>>>) depends on the implementation of the type of the source parameter. The expected behavior is that it invokes selector on each element of source to project it into an enumerable form. Each enumerable result incorporates the index of the source element. It then concatenates the enumerable results into a single, one-dimensional sequence.

The following code example demonstrates how to use SelectMany<TSource, TResult>(IQueryable<TSource>, Expression<Func<TSource, Int32, IEnumerable<TResult>>>) to perform a one-to-many projection over an array and use the index of each source element.


         class PetOwner
         {
            public string Name { get; set; }
            public List<string> Pets { get; set; }
         }

         public static void SelectManyEx2()
         {
            PetOwner[] petOwners = 
                    { new PetOwner { Name="Higa, Sidney", 
                          Pets = new List<string>{ "Scruffy", "Sam" } },
                      new PetOwner { Name="Ashkenazi, Ronen", 
                          Pets = new List<string>{ "Walker", "Sugar" } },
                      new PetOwner { Name="Price, Vernette", 
                          Pets = new List<string>{ "Scratches", "Diesel" } },
                      new PetOwner { Name="Hines, Patrick", 
                          Pets = new List<string>{ "Dusty" } } };

            // For each PetOwner element in the source array,
            // project a sequence of strings where each string
            // consists of the index of the PetOwner element in the
            // source array and the name of each pet in PetOwner.Pets.
            IEnumerable<string> query =
                petOwners.AsQueryable()
                .SelectMany(
                (petOwner, index) => petOwner.Pets.Select(pet => index + pet)
                );

            foreach (string pet in query)
               outputBlock.Text += pet + "\n";
         }

         // This code produces the following output:
         //
         // 0Scruffy
         // 0Sam
         // 1Walker
         // 1Sugar
         // 2Scratches
         // 2Diesel
         // 3Dusty



Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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