Cannot create self referential error

Question

I recently updated this application from rails 2.2.2 to 2.3.11. Everything was running fine before the upgrade. After the upgrade i am getting the following error:

ActiveRecord::HasAndBelongsToManyAssociationForeignKeyNeeded in InstrumentsController#arrow
Cannot create self referential has_and_belongs_to_many association on 'Trait#traits'. :association_foreign_key cannot be the same as the :foreign_key.

In Gift model:

class Gift < ActiveRecord::Base
  has_many :delegate_gifts
  has_many :answers

  belongs_to :feel_motive, :class_name => "Trait", :foreign_key => "feel_motive_id"
  belongs_to :see_motive, :class_name => "Trait", :foreign_key => "see_motive_id"
  belongs_to :incline_motive, :class_name => "Trait", :foreign_key => "incline_motive_id"

  has_and_belongs_to_many :users
  has_and_belongs_to_many :best_contributions

  def traits
    traits = []
    traits << feel_motive unless feel_motive.nil?
    traits << see_motive unless see_motive.nil?
    traits << incline_motive unless incline_motive.nil?
    return traits
  end
end

trait model:

class Trait < Field
  has_and_belongs_to_many :traits
end

Why does upgrading from 2.2.2 to 2.3.11 produce this error?

Answer 1

has_and_belongs_to_many can not point to itself (at least not in the easy way). That is why you have "self referential" error. If you really need this recurrent association then you have to write something like this:

class User < ActiveRecord::Base
  has_and_belongs_to_many :friends,
    :class_name => "User",
    :association_foreign_key => "friend_id",
    :join_table => "friends_users"
end

so you need additional field friend_id in users table and new join table friends_users with fields: user_id and friend_id

Note: more information you can find there: http://railsforum.com/viewtopic.php?id=4237)