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Queryable.Join(Of TOuter, TInner, TKey, TResult) Method (IQueryable(Of TOuter), IEnumerable(Of TInner), Expression(Of Func(Of TOuter, TKey)), Expression(Of Func(Of TInner, TKey)), Expression(Of Func(Of TOuter, TInner, TResult)), IEqualityComparer(Of TKey))

Correlates the elements of two sequences based on matching keys. A specified IEqualityComparer(Of T) is used to compare keys.

Namespace:  System.Linq
Assembly:  System.Core (in System.Core.dll)
'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)), _
	comparer As IEqualityComparer(Of TKey) _
) As IQueryable(Of TResult)

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(Of TOuter)

The first sequence to join.

inner
Type: System.Collections.Generic.IEnumerable(Of TInner)

The sequence to join to the first sequence.

outerKeySelector
Type: System.Linq.Expressions.Expression(Of Func(Of TOuter, TKey))

A function to extract the join key from each element of the first sequence.

innerKeySelector
Type: System.Linq.Expressions.Expression(Of Func(Of TInner, TKey))

A function to extract the join key from each element of the second sequence.

resultSelector
Type: System.Linq.Expressions.Expression(Of Func(Of TOuter, TInner, TResult))

A function to create a result element from two matching elements.

comparer
Type: System.Collections.Generic.IEqualityComparer(Of TKey)

An IEqualityComparer(Of T) to hash and compare keys.

Return Value

Type: System.Linq.IQueryable(Of TResult)
An IQueryable(Of 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(Of TOuter). 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

outer or inner or outerKeySelector or innerKeySelector or resultSelector 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 Join(Of TOuter, TInner, TKey, TResult)(IQueryable(Of TOuter), IEnumerable(Of TInner), Expression(Of Func(Of TOuter, TKey)), Expression(Of Func(Of TInner, TKey)), Expression(Of Func(Of TOuter, TInner, TResult)), IEqualityComparer(Of TKey)) method generates a MethodCallExpression that represents calling Join(Of TOuter, TInner, TKey, TResult)(IQueryable(Of TOuter), IEnumerable(Of TInner), Expression(Of Func(Of TOuter, TKey)), Expression(Of Func(Of TInner, TKey)), Expression(Of Func(Of TOuter, TInner, TResult)), IEqualityComparer(Of TKey)) itself as a constructed generic method. It then passes the MethodCallExpression to the CreateQuery(Of 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(Of TOuter, TInner, TKey, TResult)(IQueryable(Of TOuter), IEnumerable(Of TInner), Expression(Of Func(Of TOuter, TKey)), Expression(Of Func(Of TInner, TKey)), Expression(Of Func(Of TOuter, TInner, TResult)), IEqualityComparer(Of TKey)) 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 by using comparer. The outcome of the comparisons is used to create a matching pair 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.

.NET Framework

Supported in: 4.5.1, 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 8, Silverlight 8.1

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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