inherits_many

Summary

Allow many-to-many relationships to inherit associated objects from a parent object's has_many association.

Installation

Add the following to your Gemfile:

gem 'inherits_many'

Usage Example

An individual restaurant can have many menu items, but a restaurant that belongs to a chain inherits all it's menu items from the chain it belongs to. The behaviors we want include:

• When a restaurant joins a chain, it gets a copy of all the menu items from that chain.
• When a restaurant leaves a chain, all those menu items go away.
• When a menu item is added to a chain, it is added to all the restaurants in that chain.
• When a menu item is removed from a chain, it is removed from all restaurants in that chain.

The ActiveRecord associations and inherits_many definition look like this:

class Chain < ActiveRecord::Base
  has_many :restaurants
  has_many :menu_items
end

class MenuItem < ActiveRecord::Base
  has_many :restaurant_menu_items
  has_many :restaurants, through: :restaurant_menu_items
  belongs_to :chain

  # Syntax for this gem.
  passes_on_to :restaurants, of: :chain

end

class Restaurant < ActiveRecord::Base
  has_many :restaurant_menu_items
  has_many :menu_items, through: :restaurant_menu_items
  belongs_to :chain

  # Syntax for this gem.
  inherits_many :menu_items, from: :chain

end

class RestaurantMenuItem < ActiveRecord::Base
  belongs_to :restaurant
  belongs_to :menu_item
end