rails activerecord：如何指定与“belongs_to ...：class_name ...”的反向关系

Question

我的 belongs_to ... :class_name 关联工作正常，但看不到如何创建互惠关联。

这是我现在拥有的：

class Contact < ActiveRecord::Base
  # has fields email_id and phone_id
  belongs_to :email, :class_name => 'Rolodex' # this works fine
  belongs_to :phone, :class_name => 'Rolodex' # this works fine
end

class Rolodex < ActiveRecord::Base
  # entry:string  holds a phone#, email address, etc
  has_many :contacts    # does NOT WORK, since no Contact.rolodex_id field
end

并且该关联在 Contact -> Rolodex 方向上运行良好（通过名称 :phone 和 :email）

john = Contact.first
john.phone.entry
# correctly returns the person's rolodex.entry for their phone, if any
john.email.entry
# correctly returns the person's rolodex.entry for their email, if any

但是，如果我想查找共享我无法使用的 rolodex 条目的所有联系人：

r = Rolodex.first
r.contacts
# column contacts.rolodex_id does not exist

当然，我可以绕过关联，直接做查找：

Contacts.where("(email_id = ?) OR (phone_id = ?)", r.id. r.id)

但我认为有一些（更好的）方法，例如，指定belongs_to ... :class_name 关联的倒数的方法？

Answer 1

类似以下的方法会起作用：

class Rolodex < ActiveRecord::Base
  has_many :email_contacts, class_name: 'Contact', foreign_key: 'email_id'
  has_many :phone_contacts, class_name: 'Contact', foreign_key: 'phone_id'

  def contacts
    email_contacts + phone_contacts
  end
end