DevForce 2012: Multiple Field Join

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Multiple Field Join

Printed From: IdeaBlade
Category: DevForce
Forum Name: DevForce 2012
Forum Discription: For .NET 4.5
URL: http://www.ideablade.com/forum/forum_posts.asp?TID=4255
Printed Date: 03-May-2025 at 6:46pm

Topic: Multiple Field Join

Posted By: JaxGuyWestside
Subject: Multiple Field Join
Date Posted: 30-Jul-2013 at 7:55am

Hello,

I'm trying to write an DevForce LINQ query where I need to join on multiple fields. I looked in the documentation and found the examples for joins, but I didn't see an example that addressed this specific scenario. I searched the web for linq queries with multiple field joins and here is what I found which does convey what I'm trying to do; I just need to figure out how to do it for DevForce.

from x in entity

join y in entity2 on new { x.field1, x.field2 } equals new { y.field1, y.field2 }

Any help is greatly appreciated!!

Replies:

Posted By: kimj
Date Posted: 30-Jul-2013 at 12:01pm

You should first read this - http://drc.ideablade.com/devforce-2012/bin/view/Documentation/linq-join-examples - http://drc.ideablade.com/devforce-2012/bin/view/Documentation/linq-join-examples - to determine whether you really do need a join. In most models, relationships can be expressed with navigation properties, for example:

aCustomer.Orders

anOrder.Customer

If you do need to join entities which don't have an existing foreign key relationship, you can do so like you've done above. For example, here's a contrived example to join Northwind Employees and Users based on their names:

var query = from e in entityManager.Employees
             join u in entityManager.Users
             on new { id1 = e.FirstName, id2 = e.LastName } equals new { id1 = u.FirstName, id2 = u.LastName }
             select e;

var results = query.ToList();

The types and names of properties in the anonymous types used in the join must be the same, and here the "id1" and "id2" names aren't required.

Posted By: JaxGuyWestside
Date Posted: 31-Jul-2013 at 7:28pm

Thank you for the quick response. I believe that's basically what I was doing; but I must have had a syntax error of some sort that was causing the problem. At least I had the right concept.

Thanks again!

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