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Queryable.GroupJoin(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, IEnumerable(Of TInner), TResult)), IEqualityComparer(Of TKey))

Correlates the elements of two sequences based on key equality and groups the results. 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 GroupJoin(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, IEnumerable(Of 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, IEnumerable(Of TInner), TResult))
A function to create a result element from an element from the first sequence and a collection of matching elements from the second sequence.
comparer
Type: System.Collections.Generic.IEqualityComparer(Of TKey)
A comparer to hash and compare keys.

Return Value

Type: System.Linq.IQueryable(Of TResult)
An IQueryable(Of T) that contains elements of type TResult obtained by performing a grouped 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 GroupJoin(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, IEnumerable(Of TInner), TResult)), IEqualityComparer(Of TKey)) method generates a MethodCallExpression that represents calling GroupJoin(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, IEnumerable(Of 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 GroupJoin(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, IEnumerable(Of TInner), TResult)), IEqualityComparer(Of TKey)) depends on the implementation of the type of the outer parameter. The expected behavior is that 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 match each element in outer with zero or more elements from inner. Then the resultSelector function is invoked to project a result object from each group of correlated elements.

.NET Framework

Supported in: 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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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