Question

I was just looking around rails and noticed there is an app controller but no app model.

Is there no root model in rails ? if not where do you put a piece of code that needs to be in every model.

Thanks, Alex

Answer 1

Nothing says your controllers have to subclass ApplicationController but it generally is the standard because the vast majority of rails applications make use of the layout capabilities (which can vary on each controller), so instead of forcing the rare ones without layouts from turning the layout off (layout nil or layout false) for each controller, they make an ‘abstract’ one that you can turn controller features on and off easily for your whole application.

Now for models, you could create an ApplicationModel for all of your models to subclass, but there are two things to think about:

1. ActiveRecord normally detects when you subclass an already subclassed ActiveRecord::Base and uses this to turn STI (single table inheritance) on.
2. ApplicationModel will be an actual model that is expected to have a table in your database. This can lead to problems down the line.

To fix these two problems, you have to set abstract_class to true for ActiveRecord to properly function.

class ApplicationModel < ActiveRecord::Base
  self.abstract_class = true
end

In contrast to an abstract ActionController, abstract_class must set to true which means the developer must know they cannot remove this line from ApplicationModel. With ApplicationController you can do pretty much whatever you want to it.