# How do you make associations when a table has two unique columns?

**URL:** <https://www.ruby-forum.com/t/how-do-you-make-associations-when-a-table-has-two-unique-columns/166731>\
**Category:** Rails\
**Created:** [April 29, 2009, 12:38am UTC](https://www.ruby-forum.com/t/how-do-you-make-associations-when-a-table-has-two-unique-columns/166731 "2009-04-29T00:38:24Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![blgroup](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/eb8c5e/32.png) [@blgroup](https://www.ruby-forum.com/u/blgroup)\
**Post date:** [April 29, 2009, 12:38am UTC](https://www.ruby-forum.com/t/how-do-you-make-associations-when-a-table-has-two-unique-columns/166731/1 "2009-04-29T00:38:24Z")

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Having trouble with a somewhat unconventional modelling in Rails  
2.2.2.

Take three table.

1. User model with primary integer id and a unique string guid.

2. Model X has foreign key to User as integer user\_id and its model  
includes  
belongs\_to :users

3. Model Y has foreign key to User as string user\_guid and its model  
includes  
belongs\_to :users, :foreign\_key =\> ‘user\_guid’

This tells Rails which column to use in Model Y to look up Users.  
But How do I tell Rails which column to use in User?

In other words, how do I tell Rails to join (or select) from  
Users.guid instead of Users.id when referencing Y.user?

The has\_one and has\_many association has a :primary\_key option, but  
this seems to be missing on the belongs\_to association

How do people work around this? Any help would be greatly  
appreciated.

Thanks,  
=Blair.

---

<div class="post-metadata">

**Author:** ![blgroup](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/eb8c5e/32.png) [@blgroup](https://www.ruby-forum.com/u/blgroup)\
**Post date:** [April 29, 2009, 5:16am UTC](https://www.ruby-forum.com/t/how-do-you-make-associations-when-a-table-has-two-unique-columns/166731/2 "2009-04-29T05:16:59Z")

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On Tue, Apr 28, 2009 at 9:38 PM, blgroup [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> belongs\_to :users
> 
> 1. Model Y has foreign key to User as string user\_guid and its model  
> includes  
> belongs\_to :users, :foreign\_key =\> ‘user\_guid’

Are you sure you don’t mean:  
belongs\_to :user, :foreign\_key =\> ‘user\_guid’ #\<- Using singular ‘user’  
then Y.user should work fine

> How do people work around this? Any help would be greatly  
> appreciated.
> 
> Thanks,  
> =Blair.

Setup your user model like this:

class User \< ActiveRecord::Base  
set\_primary\_key :guid  
end

Andrew T.  
[http://ramblingsonrails.com](http://ramblingsonrails.com)  
[http://www.linkedin.com/in/andrewtimberlake](http://www.linkedin.com/in/andrewtimberlake)

“I have never let my schooling interfere with my education” - Mark Twain