使用不同的列名称创建Rails关联

Question

I have three models namely, Notifications, Devices and Users. Notification has registration_ids which is mapped to the token field of devices. Devices has user_id field which is mapped to the id field of User model.

How do I create as has_many_through or has_and_belongs_to_many association from Notification model to extract the user corresponding to that notification.

Moreover, I created this association in Notifications class belongs_to :device, :primary_key => 'registration_ids', :foreign_key => 'token' and this one in device class has_many :notifications, :primary_key => 'token', :foreign_key => 'registration_ids'

device class is able to recognize the notification class, while notification class is not able to recognize the device class

Following the piece of my code from notification.rb file

class Notification < Rpush::Gcm::Notification
  self.inheritance_column = nil
  belongs_to :device, :foreign_key => 'registration_ids', :primary_key => 'token'
  delegate :user, to: :device #-> notification.user.name
end

Answer 1

#app/models/notification.rb
class Notification < ActiveRecord::Base
  belongs_to :device, foreign_key: :registration_id, primary_key: :token
  delegate :user, to: :device #-> notification.user.name
end

#app/models/device.rb
class Device < ActiveRecord::Base
  belongs_to :user
  has_many :notifications, foreign_key: :registration_id, primary_key: :token
end

#app/models/user.rb
class User < ActiveRecord::Base
  has_many :devices
  has_many :notifications, through: :devices
end

The above is how I would perceive it to be set up.

You'll be able to call:

@notification = Notification.find params[:id]

@notification.device.user.name #-> "name" of associated "user" model
@notification.user.name        #-> delegate to "user" model directly

---

The delegate method is a trick to circumvent the law of demeter issue (calling an object several levels "away" from the parent).