Rails协会归属于

Question

I know sty must be wrong in the way I build my db but please take a minute answering this : I am building a supermarket model, where 1 user has a shopping list, each list has many products. So what I do is :

class User < ActiveRecord::Base
  has_many :lists
end

class List < ActiveRecord::Base
  belongs_to :user
  has_many :products
end

class Product < ActiveRecord::Base
  ????
end

A list has several products but products don't belong to lists. What should I do to have Users having many lists, and lists having many products ? regards,

Answer 1

Have a class that links them via has_many through.

class ListItem < ActiveRecord::Base
  belongs_to :list
  belongs_to :product
end

class List < ActiveRecord::Base 
  belongs_to :user 
  has_many :list_items
  has_many :products, through: :list_items
end

Answer 2

You don't need an additional class. Rails can manage this for you with the has_and_belongs_to_many_association

In your case, it would be:

class User < ActiveRecord::Base
  has_many :lists
end

class List < ActiveRecord::Base
  belongs_to :user
  has_and_belongs_to_many :products
end

class Product < ActiveRecord::Base
  has_and_belongs_to_many :lists
end

Of course, you need to add the join table in the migration:

create_table :lists_products, id: false do |t|
  t.belongs_to :list
  t.belongs_to :product
end