Rails - Jan 2007 - Two-side-polymorphic association - or: how to link multiple models to each other

Hi,

I''m planning an application with a bunch of models which can be linked
to each other. Since a few days I''m thinking about the right way to go,
to implement these model associations. First thought was, I should use
polymorphic associations, but I think it''s not enough for my case. I
came up with the idea of an explicit link model which would look like
this:

 LinkModel
----------------------------------------------------
| source_id | source_type | target_id |target_type |


There''re a few problems with this kind of association:

Every model can be a source OR a target. Let''s say I want to get every
company which is linked to a specific person (id=42), I have to do two
queries to get the ids for all companies linked to a person.

SELECT target_id FROM link_model WHERE source_type = ''person''
AND
source_id = ''42'' AND target_type = ''company''
SELECT source_id FROM link_model WHERE target_type = ''person''
AND
target_id = ''42'' AND source_type = ''company''

How do I implement this in Rails? This looks a bit like a
Two-Side-Polymorphic-Association. Is this possible? Or are there any
other ideas how to do this kind of association?

tisp


--~--~---------~--~----~------------~-------~--~----~
 You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en
-~----------~----~----~----~------~----~------~--~---

i think this might be what you are looking for:

http://wiki.rubyonrails.org/rails/pages/ManytoManyPolymorphicAssociations

On 1/11/07, tisp
<t.springmann-yM2StcZat7YdDX0dnZFiFbNAH6kLmebB@public.gmane.org>
wrote:
>
> Hi,
>
> I''m planning an application with a bunch of models which can be
linked
> to each other. Since a few days I''m thinking about the right way
to go,
> to implement these model associations. First thought was, I should use
> polymorphic associations, but I think it''s not enough for my case.
I
> came up with the idea of an explicit link model which would look like
> this:
>
>  LinkModel
> ----------------------------------------------------
> | source_id | source_type | target_id |target_type |
>
>
> There''re a few problems with this kind of association:
>
> Every model can be a source OR a target. Let''s say I want to get
every
> company which is linked to a specific person (id=42), I have to do two
> queries to get the ids for all companies linked to a person.
>
> SELECT target_id FROM link_model WHERE source_type =
''person'' AND
> source_id = ''42'' AND target_type =
''company''
> SELECT source_id FROM link_model WHERE target_type =
''person'' AND
> target_id = ''42'' AND source_type =
''company''
>
> How do I implement this in Rails? This looks a bit like a
> Two-Side-Polymorphic-Association. Is this possible? Or are there any
> other ideas how to do this kind of association?
>
> tisp
>
>
> >
>
--~--~---------~--~----~------------~-------~--~----~
 You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en
-~----------~----~----~----~------~----~------~--~---

Not exactly, but it''s a start. That solution is not truly two-sides, as
it only implements one of the above SQL statements. Also it''s not
really beautiful as I it could be?!

tisp


--~--~---------~--~----~------------~-------~--~----~
 You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en
-~----------~----~----~----~------~----~------~--~---