Question

I’m developing a ruby on rails app and I want to be able to excecute a method on every AR object before each save.

I thought I’d create a layer-super-type like this:

MyObject << DomainObject << ActiveRecord::Base 

and put in DomainObject a callback (before_save) with my special method (which basically strips all tags like ‘H1’ from the string attributes of the object).

The catch is that rails is asking for the domain_object table, which I obviously don’t have.

My second attempt was to monkeypatch active record, like this:

module ActiveRecord   class Base     def my_method .... end   end end 

And put that under the lib folder.

This doesnt work, it tells me that my_method is undefined.

Any ideas?

Answer 1

Try using an abstract class for your domain object.

class DomainObject < ActiveRecord::Base   self.abstract_class = true   # your stuff goes here end 

With an abstract class, you are creating a model which cannot have objects (cannot be instantiated) and don’t have an associated table.

From reading Rails: Where to put the ‘other’ files from Strictly Untyped,

Files in lib are not loaded when Rails starts. Rails has overridden both Class.const_missing and Module.const_missing to dynamically load the file based on the class name. In fact, this is exactly how Rails loads your models and controllers.

so placing the file in the lib folder, it will not be run when Rails starts and won’t monkey patch ActiveRecord::Base. You could place the file in config/initializers, but I think there are better alternatives.