Queryable.Join<TOuter, TInner, TKey, TResult> Method (IQueryable<TOuter>, IEnumerable<TInner>, Expression<Func<TOuter, TKey>>, Expression<Func<TInner, TKey>>, Expression<Func<TOuter, TInner, TResult>>)
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Correlates the elements of two sequences based on matching keys. The default equality comparer is used to compare keys.
Namespace: System.Linq
Assembly: System.Core (in System.Core.dll)
Syntax
'Declaration
<ExtensionAttribute> _
Public Shared Function Join(Of TOuter, TInner, TKey, TResult) ( _
outer As IQueryable(Of TOuter), _
inner As IEnumerable(Of TInner), _
outerKeySelector As Expression(Of Func(Of TOuter, TKey)), _
innerKeySelector As Expression(Of Func(Of TInner, TKey)), _
resultSelector As Expression(Of Func(Of TOuter, TInner, TResult)) _
) As IQueryable(Of TResult)
public static IQueryable<TResult> Join<TOuter, TInner, TKey, TResult>(
this IQueryable<TOuter> outer,
IEnumerable<TInner> inner,
Expression<Func<TOuter, TKey>> outerKeySelector,
Expression<Func<TInner, TKey>> innerKeySelector,
Expression<Func<TOuter, TInner, TResult>> resultSelector
)
Type Parameters
- TOuter
The type of the elements of the first sequence.
- TInner
The type of the elements of the second sequence.
- TKey
The type of the keys returned by the key selector functions.
- TResult
The type of the result elements.
Parameters
- outer
Type: System.Linq.IQueryable<TOuter>
The first sequence to join.
- inner
Type: System.Collections.Generic.IEnumerable<TInner>
The sequence to join to the first sequence.
- outerKeySelector
Type: System.Linq.Expressions.Expression<Func<TOuter, TKey>>
A function to extract the join key from each element of the first sequence.
- innerKeySelector
Type: System.Linq.Expressions.Expression<Func<TInner, TKey>>
A function to extract the join key from each element of the second sequence.
- resultSelector
Type: System.Linq.Expressions.Expression<Func<TOuter, TInner, TResult>>
A function to create a result element from two matching elements.
Return Value
Type: System.Linq.IQueryable<TResult>
An IQueryable<T> that has elements of type TResult obtained by performing an inner join on two sequences.
Usage Note
In Visual Basic and C#, you can call this method as an instance method on any object of type IQueryable<TOuter>. When you use instance method syntax to call this method, omit the first parameter.
Exceptions
| Exception | Condition |
|---|---|
| ArgumentNullException | outer or inner or outerKeySelector or innerKeySelector or resultSelector 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 Join<TOuter, TInner, TKey, TResult>(IQueryable<TOuter>, IEnumerable<TInner>, Expression<Func<TOuter, TKey>>, Expression<Func<TInner, TKey>>, Expression<Func<TOuter, TInner, TResult>>) method generates a MethodCallExpression that represents calling Join<TOuter, TInner, TKey, TResult>(IQueryable<TOuter>, IEnumerable<TInner>, Expression<Func<TOuter, TKey>>, Expression<Func<TInner, TKey>>, Expression<Func<TOuter, TInner, TResult>>) itself as a constructed generic method. It then passes the MethodCallExpression to the CreateQuery<TElement>(Expression) method of the IQueryProvider represented by the Provider property of the outer parameter.
The query behavior that occurs as a result of executing an expression tree that represents calling Join<TOuter, TInner, TKey, TResult>(IQueryable<TOuter>, IEnumerable<TInner>, Expression<Func<TOuter, TKey>>, Expression<Func<TInner, TKey>>, Expression<Func<TOuter, TInner, TResult>>) depends on the implementation of the type of the outer parameter. The expected behavior is that of an inner join. The outerKeySelector and innerKeySelector functions are used to extract keys from outer and inner, respectively. These keys are compared for equality to match elements from each sequence. A pair of elements is stored for each element in inner that matches an element in outer. Then the resultSelector function is invoked to project a result object from each pair of matching elements.
Examples
The following code example demonstrates how to use Join<TOuter, TInner, TKey, TResult>(IQueryable<TOuter>, IEnumerable<TInner>, Expression<Func<TOuter, TKey>>, Expression<Func<TInner, TKey>>, Expression<Func<TOuter, TInner, TResult>>) to perform an inner join of two sequences based on a common key.
Structure Person
Public Name As String
End Structure
Structure Pet
Public Name As String
Public Owner As Person
End Structure
Shared Sub JoinEx1()
Dim magnus As New Person With {.Name = "Hedlund, Magnus"}
Dim terry As New Person With {.Name = "Adams, Terry"}
Dim charlotte As New Person With {.Name = "Weiss, Charlotte"}
Dim barley As New Pet With {.Name = "Barley", .Owner = terry}
Dim boots As New Pet With {.Name = "Boots", .Owner = terry}
Dim whiskers As New Pet With {.Name = "Whiskers", .Owner = charlotte}
Dim daisy As New Pet With {.Name = "Daisy", .Owner = magnus}
Dim people As New List(Of Person)(New Person() {magnus, terry, charlotte})
Dim pets As New List(Of Pet)(New Pet() {barley, boots, whiskers, daisy})
' Join the list of Person objects and the list of Pet objects
' to create a list of person-pet pairs where each element is
' an anonymous type that contains pet's name and the name of the
' Person object that owns the pet.
Dim query = people.AsQueryable().Join(pets, _
Function(person) person, _
Function(pet) pet.Owner, _
Function(person, pet) _
New With {.OwnerName = person.Name, .Pet = pet.Name})
Dim output As New System.Text.StringBuilder
For Each obj In query
output.AppendLine(String.Format( _
"{0} - {1}", obj.OwnerName, obj.Pet))
Next
' Display the output.
outputBlock.Text &= output.ToString() & vbCrLf
End Sub
' This code produces the following output:
' Hedlund, Magnus - Daisy
' Adams, Terry - Barley
' Adams, Terry - Boots
' Weiss, Charlotte - Whiskers
class Person
{
public string Name { get; set; }
}
class Pet
{
public string Name { get; set; }
public Person Owner { get; set; }
}
public static void JoinEx1()
{
Person magnus = new Person { Name = "Hedlund, Magnus" };
Person terry = new Person { Name = "Adams, Terry" };
Person charlotte = new Person { Name = "Weiss, Charlotte" };
Pet barley = new Pet { Name = "Barley", Owner = terry };
Pet boots = new Pet { Name = "Boots", Owner = terry };
Pet whiskers = new Pet { Name = "Whiskers", Owner = charlotte };
Pet daisy = new Pet { Name = "Daisy", Owner = magnus };
List<Person> people = new List<Person> { magnus, terry, charlotte };
List<Pet> pets = new List<Pet> { barley, boots, whiskers, daisy };
// Join the list of Person objects and the list of Pet objects
// to create a list of person-pet pairs where each element is
// an anonymous type that contains the name of pet and the name
// of the person that owns the pet.
var query = people.AsQueryable().Join(pets,
person => person,
pet => pet.Owner,
(person, pet) =>
new { OwnerName = person.Name, Pet = pet.Name });
foreach (var obj in query)
{
outputBlock.Text += String.Format(
"{0} - {1}",
obj.OwnerName,
obj.Pet) + "\n";
}
}
/*
This code produces the following output:
Hedlund, Magnus - Daisy
Adams, Terry - Barley
Adams, Terry - Boots
Weiss, Charlotte - Whiskers
*/
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.