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Queryable.SelectMany(Of TSource, TResult) Method (IQueryable(Of TSource), Expression(Of Func(Of TSource, IEnumerable(Of TResult))))

Projects each element of a sequence to an IEnumerable(Of T) and combines the resulting sequences into one sequence.

Namespace:  System.Linq
Assembly:  System.Core (in System.Core.dll)
'Declaration
<ExtensionAttribute> _
Public Shared Function SelectMany(Of TSource, TResult) ( _
	source As IQueryable(Of TSource), _
	selector As Expression(Of Func(Of TSource, IEnumerable(Of TResult))) _
) As IQueryable(Of TResult)

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(Of TSource)
A sequence of values to project.
selector
Type: System.Linq.Expressions.Expression(Of Func(Of TSource, IEnumerable(Of TResult)))
A projection function to apply to each element.

Return Value

Type: System.Linq.IQueryable(Of TResult)
An IQueryable(Of 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(Of TSource). When you use instance method syntax to call this method, omit the first parameter.
ExceptionCondition
ArgumentNullException

source or selector is Nothing.

This method has at least one parameter of type Expression(Of TDelegate) whose type argument is one of the Func(Of T, TResult) types. For these parameters, you can pass in a lambda expression and it will be compiled to an Expression(Of TDelegate).

The SelectMany(Of TSource, TResult)(IQueryable(Of TSource), Expression(Of Func(Of TSource, IEnumerable(Of TResult)))) method generates a MethodCallExpression that represents calling SelectMany(Of TSource, TResult)(IQueryable(Of TSource), Expression(Of Func(Of TSource, IEnumerable(Of 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(Of TSource, TResult)(IQueryable(Of TSource), Expression(Of Func(Of TSource, IEnumerable(Of 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. It then concatenates the enumerable results into a single, one-dimensional sequence.

The following code example demonstrates how to use SelectMany(Of TSource, TResult)(IQueryable(Of TSource), Expression(Of Func(Of TSource, IEnumerable(Of TResult)))) to perform a one-to-many projection over an array.


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

   Shared Sub SelectManyEx1()
      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"}}}

      ' Query using SelectMany().
      Dim query1 As IEnumerable(Of String) = _
                  petOwners.AsQueryable().SelectMany(Function(petOwner) petOwner.Pets)

      Dim output As New System.Text.StringBuilder("Using SelectMany():" & vbCrLf)
      ' Only one foreach loop is required to iterate through 
      ' the results because it is a one-dimensional collection.
      For Each pet As String In query1
         output.AppendLine(pet)
      Next

      ' This code shows how to use Select() instead of SelectMany().
      Dim query2 As IEnumerable(Of String()) = _
                  petOwners.AsQueryable().Select(Function(petOwner) petOwner.Pets)

      output.AppendLine(vbCrLf & "Using Select():")
      ' Notice that two foreach loops are required to iterate through 
      ' the results because the query returns a collection of arrays.
      For Each petArray() As String In query2
         For Each pet As String In petArray
            output.AppendLine(pet)
         Next
      Next

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

   ' This code produces the following output:

   ' Using SelectMany():
   ' Scruffy
   ' Sam
   ' Walker
   ' Sugar
   ' Scratches
   ' Diesel

   ' Using Select():
   ' Scruffy
   ' Sam
   ' Walker
   ' Sugar
   ' Scratches
   ' Diesel



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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