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How to add a has_many association on all models

Answer 1

A:

take a look at unloadable it may help you

Salil 2010-04-22 14:04:05

That blog post was interesting, but it didn't solve my problems. See my comments on the initial question as to why :)

joshsz 2010-04-22 14:28:13

Answer 2

A:

It's recommended to make each association in each model! It's a useless DRY way to make such things! At all, It's my opinion!

amrnt 2010-04-22 14:06:35

Answer 3

+5 A:

You state that you have many models, all of which require this association. If it were me, I'd would go with the approach of creating a base model class that contains the association and then have all the other models inherit from it. Something like:

class NotableModel < ActiveRecord::Base

  # Prevents ActiveRecord from looking for a database table for this class
  self.abstract_class = true

  has_many :notes, :as => :notable
  accepts_nested_attributes_for :notes  
end

class Foo < NotableModel
  ...
end

class Bar < NotableModel
  ...
end

In my opinion this approach is more self-documenting compared to using a little bit of metaprogramming hidden away in an initializer.

John Topley 2010-04-22 14:41:38

I agree - explicitly define this in a base class or an included module.

Jonathan Julian 2010-04-22 14:57:07

This method works, but it changes the inheritance chain. Generally that's fine, but I like the DRYer method

joshsz 2010-04-22 14:57:54

This is DRY; what do you think is being repeated?

John Topley 2010-04-22 15:17:32

@joshsz, this is DRY and far better than duck punching ActiveRecord::Base

macek 2010-04-22 19:20:07

Especially because this new base class can be extended with other methods or properties that might be useful for all of your models.

Tilendor 2010-04-22 20:33:45

If this application didn't have the requirements I've enumerated in comments to my answer below, this would absolutely be the right way to do this. It's only because this is a common practice for this application that I consider my method more 'correct'. FWIW, it is in practice repeating yourself to change the base class for a model from ActiveRecord::Base to NotableModel. Also it is technically possible (although admittedly unlikely) in this case for a developer to create a model and then forget to change its parent class, thereby not following the design tenets.

joshsz 2010-04-23 12:58:20

Answer 4

A:

Thanks to Rich Kilmer (of InfoEther), we found the elegant (and slightly opaque) way of fixing this:

# config/initializers/has_many_notes.rb
module ActiveRecord
  class Base
    def self.inherited(klass)
      super
      klass.send :has_many, :notes, :as => :notable
      klass.send :accepts_nested_attributes_for, :notes
    end
  end
end

Now no inheritance changes, and it's very DRY

joshsz 2010-04-22 14:56:54

@joshsz, chances are, you'll encounter a model that you don't want to be `Notable` at some point. This is no less DRY than @John Topley's method. Plus, if you're so hung up on being DRY, you should also adhere to **Convention Over Configuration**. Your method is cryptic and non-self-documenting.

macek 2010-04-22 19:45:06

DRY is not what you are doing. Every model currently inherits from ActiveRecord::Base. Making it inherit from a NotableModel does not add any repetition at all, its the exact same amount.Moving this Model related code away from the model folder is not intuitive at all. It absolutely works, don't get me wrong, but thinking of someone else approaching your code, I would have to do some hunting to find this. Inheritance exists to solve exactly this kind of problem. Inheritance should be preferred to monkey patching.

Tilendor 2010-04-22 20:40:07

This is the correct solution for this project, but only for the following reasons:1) This project has other full codebase cross-cutting concerns (events, for example) that are handled in the same way.2) The tenets of this domain state that *everything* must always be notable, even (potentially) notes. Whether we surface the functionality per-model is a decision to be made later, but still a possibility.3) It's not uncommon to extend core classes. If you consider this a core extension, it's suddenly a little less weird.

joshsz 2010-04-23 12:54:25

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How to add a has_many association on all models

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