Rails 4 HABTM has_many：through

Question

Team, looking for some help for a very specific (newbie) situation on a Rails 4 association. We have 3 models:

class Brand < ActiveRecord::Base
 has_many :lines, dependent: :destroy
 has_many :products, through: :lines, dependent: :destroy
end

class Line < ActiveRecord::Base
 belongs_to :brand
 has_and_belongs_to_many :products
end

class Product < ActiveRecord::Base
 has_and_belongs_to_many :lines
 has_many :brands, through: :lines
end

This configuration works well when trying to check for Products under specific Brand (or Line ) and viceversa: different Brands (or Lines ) available for a specific Product . However, when it comes to delete/destroy there is an issue. We are getting this Rspec error:

ActiveRecord::HasManyThroughCantAssociateThroughHasOneOrManyReflection:
Cannot modify association 'Brand#products' because the source reflection 
class 'Product' is associated to 'Line' via :has_and_belongs_to_many.

We have made research on this exception, checked for Rails API, with no luck, examples found are showing a different model configuration. What's missing on this approach?

Appreciate your help guys!

Answer 1

In my opinion, it should be something like this:

class Brand < ActiveRecord::Base
 has_many :lines, dependent: :destroy
 has_many :products, through: :lines, dependent: :destroy
end

class Line < ActiveRecord::Base
 belongs_to :brand
 has_and_belongs_to_many :products
end

class Product < ActiveRecord::Base
 belongs_to :brand, through: :line
 has_and_belongs_to_many :lines
end

And in migrations:

create_table :brands , force: true do |t|
  t.string :name
  ...
  t.timestamps null: false    
end

create_table :lines , force: true do |t|
  t.string :name
  t.belongs_to :brand
  ...
  t.timestamps null: false    
end

create_table :products , force: true do |t|
  t.string :name
  ...
  t.timestamps null: false    
end

create_table :line_products, force: true, id: false do |t|
  t.belongs_to :line, index: true
  t.belongs_to :product, index: true
end

I hope it will help.