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)

Syntax

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

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.

Exceptions

Exception Condition
ArgumentNullException

source or selector 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, 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.

Examples

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.

   Structure PetOwner
      Public Name As String
      Public Pets() As String
   End Structure

   Shared Sub SelectManyEx2()
      Dim petOwners() As PetOwner = _
          {New PetOwner With _
           {.Name = "Higa, Sidney", .Pets = New String() {"Scruffy", "Sam"}}, _
           New PetOwner With _
           {.Name = "Ashkenazi, Ronen", .Pets = New String() {"Walker", "Sugar"}}, _
           New PetOwner With _
           {.Name = "Price, Vernette", .Pets = New String() {"Scratches", "Diesel"}}, _
           New PetOwner With _
           {.Name = "Hines, Patrick", .Pets = New 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.
      Dim query As IEnumerable(Of String) = _
          petOwners.AsQueryable() _
          .SelectMany(Function(petOwner, index) petOwner.Pets.Select(Function(pet) index.ToString() + pet))

      Dim output As New System.Text.StringBuilder
      For Each pet As String In query
         output.AppendLine(pet)
      Next

      ' Display the output.
      outputBlock.Text &= output.ToString() & vbCrLf
   End Sub

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

         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

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.