# Overriding model associations

**URL:** <https://www.ruby-forum.com/t/overriding-model-associations/116690>\
**Category:** Engines\
**Created:** [October 8, 2007, 7:36pm UTC](https://www.ruby-forum.com/t/overriding-model-associations/116690 "2007-10-08T19:36:49Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![Sean\_Schofield](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/22d042/32.png) [@Sean\_Schofield](https://www.ruby-forum.com/u/Sean_Schofield)\
**Post date:** [October 8, 2007, 7:36pm UTC](https://www.ruby-forum.com/t/overriding-model-associations/116690/1 "2007-10-08T19:36:49Z")

</div>

I seem to recall reading that engines will not allow you to override  
your plugin models in the main application. Is that true? If so, is  
there a simple hack that would allow me to override an association?

I have the following defined in my plugin

class Tag \< ActiveRecord::Base  
has\_many\_polymorphs :taggables,  
:from =\> [:products],  
:through =\> :taggings,  
:dependent =\> :destroy  
end

This is fine except my host app uses has\_many\_polymorphs (HMP) plugin  
for tagging of other stuff. The problem is the association needs to  
include the additional classes in my main app. So I need something  
app specific:

class Tag \< ActiveRecord::Base  
has\_many\_polymorphs :taggables,  
:from =\> [:photos, :products],  
:through =\> :taggings,  
:dependent =\> :destroy  
end

Obviously I don’t want to change this in the plugin. What are my  
options?

Regards,

Sean

---

<div class="post-metadata">

**Author:** ![Sean\_Schofield](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/22d042/32.png) [@Sean\_Schofield](https://www.ruby-forum.com/u/Sean_Schofield)\
**Post date:** [October 9, 2007, 9:51am UTC](https://www.ruby-forum.com/t/overriding-model-associations/116690/2 "2007-10-09T09:51:55Z")

</div>

On Mon, Oct 08, 2007 at 01:36:32PM -0400, Sean Schofield wrote:

> I seem to recall reading that engines will not allow you to override  
> your plugin models in the main application. Is that true?

It won’t work properly with autoloading. You’ll have to it manually.  
Just put

require\_dependency  
“#{RAILS\_ROOT}/vendor/plugins/my\_engine/app/models/my\_model.rb”

just before the class definition in RAILS\_ROOT/app/models.

James, this seems to be a FAQ. Can you include it on the website’s  
FAQ page? Thanks.

Regards,  
Peter B.  
Solide ICT - [http://www.solide-ict.nl](http://www.solide-ict.nl)

---

<div class="post-metadata">

**Author:** ![Sean\_Schofield](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/22d042/32.png) [@Sean\_Schofield](https://www.ruby-forum.com/u/Sean_Schofield)\
**Post date:** [October 9, 2007, 4:16pm UTC](https://www.ruby-forum.com/t/overriding-model-associations/116690/3 "2007-10-09T16:16:42Z")

</div>

Weird. I decided to test the default behavior before trying your  
suggestion and it worked the opposite of how its been documented. My  
app/models/Tag.rb loaded in place of plugin/models/Tag.rb. I can’ say  
for sure which order the classes were loaded in but the end result was  
that the associations created by the plugin version were ignored in  
favor of the ones created in my app model.

Perhaps this is unique to HMP? In any event, its good to know the  
workaround which I’m sure to need at some future point. I also agree  
it should go in FAQ (along with a description of the load order for  
views, helpers and controllers.)

Thanks for the help.

Sean

---

<div class="post-metadata">

**Author:** ![Sean\_Schofield](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/22d042/32.png) [@Sean\_Schofield](https://www.ruby-forum.com/u/Sean_Schofield)\
**Post date:** [October 9, 2007, 4:31pm UTC](https://www.ruby-forum.com/t/overriding-model-associations/116690/4 "2007-10-09T16:31:23Z")

</div>

On Tue, Oct 09, 2007 at 10:16:00AM -0400, Sean Schofield wrote:

> Weird. I decided to test the default behavior before trying your  
> suggestion and it worked the opposite of how its been documented. My  
> app/models/Tag.rb loaded in place of plugin/models/Tag.rb.

That’s correct, and as far as I know that’s exactly how it’s documented.  
It will load that model _instead_ of the one in your engine, as opposed  
to _mixing it in_ with the engine code, which is what happens with the  
controllers and helpers. This means that any methods defined on the  
model class in your engine will not be available from the application.

That’s why you need to manually add a require\_dependency call just  
before  
defining your model. That way, the model class definition “opens up”  
the  
existing class from your engine. This is what happens automatically in  
the case of Controllers or Helpers.

Hope this explanation is a little clearer,  
Peter B.  
Solide ICT - [http://www.solide-ict.nl](http://www.solide-ict.nl)