Shopping cart Active Record Associations-CodePudding

I am trying to implement a shopping cart within a Rails application. For this, I am trying to glue together these models:

user.rb

class User < ApplicationRecord
  has_many :cart_contents
end

cart_content.rb:

class CartContent < ApplicationRecord
  belongs_to :user
  has_one :product
end

product.rb

class Product < ApplicationRecord
end

To test if this arrangement is working, I tried this in the console:

irb(main):006:0> cc = CartContent.new
=> 
#<CartContent:0x000055679d802a28
...

irb(main):008:0> cc.user = User.find(1)
  User Load (0.2ms)  SELECT "users".* FROM [...]
=> #<User id: 1, email: "[email protected]", ...

irb(main):010:0> cc.product = Product.find(1)
  Product Load (0.1ms)  SELECT "products".* FROM [...]                                                                      
/[...]/activemodel-7.0.0/lib/active_model/attribute.rb:211:
in `with_value_from_database': can't write unknown attribute `cart_content_id` (ActiveModel::MissingAttributeError)

What am I missing here? Do I need to indicate a relationship to cart_content in product.rb?

CodePudding user response：

One possible solution: you may want your CartContent to belongs_to :product.

class CartContent < ApplicationRecord
  belongs_to :user
  has_one :product # change this to belongs_to
end

cc.product = Product.find(1)

# .. can't write unknown attribute `cart_content_id` (ActiveModel::MissingAttributeError)

has_one will expect your products table to have a cart_content_id column.

See guide section 2.7 Choosing Between belongs_to and has_one

CodePudding user response：

For this, you need to build relations between your models. As mentioned by Jared in this link for the foreign key to exist, you need to specify a belongs_to constraint.

The distinction is in where you place the foreign key (it goes on the table for the class declaring the belongs_to association)

class Product < ApplicationRecord
  belongs_to :cart_content
end

If you also want to access all Products for User you can go for below, but you probably don't need a through relation.

class User < ApplicationRecord
  has_many :cart_contents
  has_many :products, through: :cart_contents
end

Then your Product model would look like this

class Product < ApplicationRecord
  belongs_to :cart_content
  belongs_to :user
end