Queryable.SelectMany<TSource, TResult> Method (IQueryable<TSource>, Expression<Func<TSource, IEnumerable<TResult>>>)
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Projects each element of a sequence to an IEnumerable<T> and combines the resulting sequences into one sequence.
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, IEnumerable(Of TResult))) _
) As IQueryable(Of TResult)
public static IQueryable<TResult> SelectMany<TSource, TResult>(
this IQueryable<TSource> source,
Expression<Func<TSource, 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, IEnumerable<TResult>>>
A projection function to apply to each 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.
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, IEnumerable<TResult>>>) method generates a MethodCallExpression that represents calling SelectMany<TSource, TResult>(IQueryable<TSource>, Expression<Func<TSource, 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, 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. 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, IEnumerable<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
class PetOwner
{
public string Name { get; set; }
public List<String> Pets { get; set; }
}
public static void SelectManyEx1()
{
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" } } };
// Query using SelectMany().
IEnumerable<string> query1 =
petOwners.AsQueryable().SelectMany(petOwner => petOwner.Pets);
outputBlock.Text += "Using SelectMany():" + "\n";
// Only one foreach loop is required to iterate through the
// results because it is a one-dimensional collection.
foreach (string pet in query1)
outputBlock.Text += pet + "\n";
// This code shows how to use Select() instead of SelectMany().
IEnumerable<List<String>> query2 =
petOwners.AsQueryable().Select(petOwner => petOwner.Pets);
outputBlock.Text += "\nUsing Select():" + "\n";
// Notice that two foreach loops are required to iterate through
// the results because the query returns a collection of arrays.
foreach (List<String> petList in query2)
{
foreach (string pet in petList)
{
outputBlock.Text += pet + "\n";
}
outputBlock.Text += "\n";
}
}
/*
This code produces the following output:
Using SelectMany():
Scruffy
Sam
Walker
Sugar
Scratches
Diesel
Using Select():
Scruffy
Sam
Walker
Sugar
Scratches
Diesel
*/
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.