Question

I have 3 models. These are the User, Product and Price model. I want Users to be able to subscribe to Products and watch the Price model for lower prices. I’m thinking about how to set this up but haven’t figured out the correct associations.

My associations as of now are like this:

Note: Many fields (table columns as well) have been erased for simplicity

class User
  has_many :prices, :dependent => :destroy
  has_many :products, :through => :prices
end

class Product
  # table columns - :name
  has_many :prices
  has_many :users, :through => :prices
end

class Price 
  # table columns - :cost, :user_id, :product_id, :store_id
  belongs_to :user
  belongs_to :product
  belongs_to :store
end

I was going to set this up by making a boolean in the Product model called :watch_product but I get stuck at the associations. Should I give Product a user_id or the other way around? I have a :through association but no user_id on Product or a product_id on User. Should the watch_product go on the Price instead?

Answer 1

I would not store the user information in the Price model. I would introduce a separate model for storing user to product subscription.

class User
  has_many :user_products
  has_many :products, :through => :user_products
  has_many :prices, :through => :products 
end

class UserProduct
  belongs_to :user
  belongs_to :product
end

class Product
  has_many :prices
  has_many :user_products
  has_many :users, :through => :user_products
end

class Price 
  # table columns - :cost, :product_id, :store_id
  belongs_to :product
  belongs_to :store

  scope :by_product, lambda {|product| where(:product_id => product)}
  scope :by_store, lambda {|store| where(:store_id => store)}
end

Now you can get the prices for user as follows:

user.prices.by_product(12)
user.prices.by_store(10)
user.prices.by_product(12).by_store(10)