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

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)

static member Join : 
        outer:IQueryable<'TOuter> * 
        inner:IEnumerable<'TInner> * 
        outerKeySelector:Expression<Func<'TOuter, 'TKey>> * 
        innerKeySelector:Expression<Func<'TInner, 'TKey>> * 
        resultSelector:Expression<Func<'TOuter, 'TInner, 'TResult>> -> IQueryable<'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(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. 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 a null reference (Nothing in Visual Basic).

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.

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.

No code example is currently available or this language may not be supported.

.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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