ruby-on-rails - 无法创建自引用错误

Question

我最近将这个应用程序从 rails 2.2.2 更新到 2.3.11。升级前一切正常。升级后，我收到以下错误:

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.

在礼物模型中:

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

特质模型:

class Trait < Field
  has_and_belongs_to_many :traits
end

为什么从 2.2.2 升级到 2.3.11 会产生这个错误？

Answer 1

has_and_belongs_to_many不能指向自己(至少不是以简单的方式)。这就是为什么你有“自我引用”错误的原因。如果你真的需要这个循环关联，那么你必须这样写:

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

所以你需要额外的字段 friend_id在用户表和新连接表friends_users 中，字段为: user_id和 friend_id
注意:您可以在此处找到更多信息: http://railsforum.com/viewtopic.php?id=4237 )