Rails: is it possible to add extra attribute to a has_and_belongs_to_many association?

Question

What I mean is if I have two models, connected by a has_and_belongs_to_many association, can I store other data in the join table for each association? That is, the extra data w

Answer 1

Short answer no you cannot with a HABTM relationship. It is only intended for simple many to many relationships.

You will need to use a has_many :through relationship. In this scenario you will create a join model (PartPackage) where you can define the extra attributes that you need.

class Part < ActiveRecord::Base
  has_many :part_packages
  has_many :packages, :through => :part_packages

  has_and_belongs_to_many :assemblies
  belongs_to :user

  validates :name, :user_id, :presence => true
end

class PartPackage < ActiveRecord::Base
  belongs_to :part
  belongs_to :package
end

class Package < ActiveRecord::Base
  has_many :part_packages
  has_many :parts, :through => :part_packages
  belongs_to :user
end