# Why do models behave this way?

**URL:** <https://www.ruby-forum.com/t/why-do-models-behave-this-way/52137>\
**Category:** Engines Development\
**Created:** [January 11, 2006, 9:30am UTC](https://www.ruby-forum.com/t/why-do-models-behave-this-way/52137 "2006-01-11T09:30:06Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![subimage](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/aca169/32.png) [@subimage](https://www.ruby-forum.com/u/subimage)\
**Post date:** [January 11, 2006, 9:30am UTC](https://www.ruby-forum.com/t/why-do-models-behave-this-way/52137/1 "2006-01-11T09:30:06Z")

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## From the wiki…

Because Engines takes care of some of the load path, Ruby itself will  
search for these files in order, and load the very first one it finds.  
The paths this search will check are, in order:

```
* your app/models directory
* your lib directory
* the app/models directories in each engine, in active order
* the lib directories (and subdirectories) of each engine, in active 

```

## order.

Why is it that models act like this? I would expect that you could place  
a model in your app/models directory and override/add methods (just like  
controllers).

Technical limitations? Design flaw?

Curious…thanks.

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**Author:** ![subimage](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/aca169/32.png) [@subimage](https://www.ruby-forum.com/u/subimage)\
**Post date:** [January 11, 2006, 10:58am UTC](https://www.ruby-forum.com/t/why-do-models-behave-this-way/52137/2 "2006-01-11T10:58:36Z")

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Apparently this bit of documentation hasn’t survived the transition to  
the new wiki:

The ‘code merging’ that the Engines plugin does works for helpers and  
controllers because of the naming convention the files containing  
those classes have (whatever\_controller… whatever\_helper.rb and so  
on). The Engines plugin overrides the loading mechanism so that when  
one of those files is loaded, it merges the code with any similarly  
named controllers in well-known places within your engines directory.

There is no such naming convention for models (or any other ruby  
files), so there’s no way to determine where any other corresponding  
files might be. If you asked ruby/rails to “require ‘guid’”, there’s  
no way to determine just from the filename (and that’s all we have)  
whether or not it’s a model from /app/models, a lib from /lib, or from  
somewhere in /vendor (or anywhere else on the loadpath). Shy of going  
through the WHOLE load path searching for similarly-named files and  
loading them, there’s nothing we can do - and doing that would be a  
spectacularly bad idea:

- it would be very slow
- it would risk loading unnecessary files along with all their  
dependencies - imagine looking for your ‘widget’ class and having a  
whole bunch of GUI code loaded into memory just because it contains a  
class of the same name.

So - technical limitations. Or ‘design flaw of Rails’ if you feel they  
should’ve named the model files whatever\_model.rb.

The solution I’d suggest, and that I’ve tried to present in the login  
and user engines, is not actually putting any code into model classes  
directly. Instead, create modules which can then be included into  
model classes. To override the User class in the login engine, you  
only have to create a user.rb in your /app/models directory, and  
ensure that it has the line “include  
‘LoginEngine::AuthenticatedUser’”. To override any methods defined in  
the module, just redefine them in your class.

Hope this makes it a bit clearer.

- james

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**Author:** ![subimage](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/aca169/32.png) [@subimage](https://www.ruby-forum.com/u/subimage)\
**Post date:** [January 11, 2006, 5:04pm UTC](https://www.ruby-forum.com/t/why-do-models-behave-this-way/52137/3 "2006-01-11T17:04:01Z")

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James A. wrote:

> The solution I’d suggest, and that I’ve tried to present in the login  
> and user engines, is not actually putting any code into model classes  
> directly. Instead, create modules which can then be included into  
> model classes. To override the User class in the login engine, you  
> only have to create a user.rb in your /app/models directory, and  
> ensure that it has the line “include  
> ‘LoginEngine::AuthenticatedUser’”. To override any methods defined in  
> the module, just redefine them in your class.
> 
> Hope this makes it a bit clearer.

A lot - thanks. Hopefully this info makes it back to the wiki as well…

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**Author:** ![subimage](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/aca169/32.png) [@subimage](https://www.ruby-forum.com/u/subimage)\
**Post date:** [January 11, 2006, 5:33pm UTC](https://www.ruby-forum.com/t/why-do-models-behave-this-way/52137/4 "2006-01-11T17:33:07Z")

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Feel free to post it up 🙂

- james

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**Author:** ![subimage](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/aca169/32.png) [@subimage](https://www.ruby-forum.com/u/subimage)\
**Post date:** [January 13, 2006, 12:13am UTC](https://www.ruby-forum.com/t/why-do-models-behave-this-way/52137/5 "2006-01-13T00:13:50Z")

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James A. wrote:

> Feel free to post it up 🙂
> 
> - james

It’s there…modified the developer page a little as well.