Learning deep associations in models

Wael Nasreddine
2011-05-24T10:06:22Z

Hello,

I''m a web developer comping from Zend Framework and I''m trying
to learn
Rails the right way and avoid Bad Practice from the start.

I have a few questions in my head that I''m unable to get answered on my
own, so I''m going to try and get it explained with an example.

Let''s say I''m building a site for a restaurant and the website
have a
Menu model (which is essentially categories, like Pizza, Burgers etc..),
a Product model that belongs to the menu and an Ingredient model which
belongs to Product, code:

class Menu < ActiveRecord::Base
  has_many :products

  # … validations and other logic
end

class Product < ActiveRecord::Base
  belongs_to :menu
  has_many :ingredients

  accepts_nested_attributes_for :ingredients

  # … validations and other logic
end

class Ingredient < ActiveRecord::Base
  belongs_to :product

  validates :name, :presence => true, :unique => true

  # … other validations and other logic.
end

So far so good, however now I''m stuck because I''m not sure how
to code
what I have in mind without ending up with a spaghetti code. In the new
product form, I would like the user to be able to add ingredients (
accepts_nested_attributes_for already there so I should be good for
having the fields in the form ) but when the form has been filled and
submitted, I want to create an ingredient if and only if it does not
already exists, if on the other hand, it does, in this case the
association should happen on the one that already exists, for example:

Let''s say that I already have :onion in the ingredients table, if I
added a new product that has onion, I should not have two rows for the
:onion ingredient (should not happen since I added a validation), but
instead the association should happen on the one that already exists..

How can I accomplish that? Should I be using a before_create hook? What
should I do in that hook? or should I create a custom create method?

Thank you.

Wael

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