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

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.
        MsgBox(output.ToString())
    End Sub 

    ' This code produces the following output: 

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

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

.NET Framework

Supported in: 4.5, 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

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