Rails多态has_many关联

Question

Is it possible to have a polymorphic "has_many" association in rails?

I had a table notifications which had a communication_method that could be either an email address or a phone number:

change_table :notifications do |t|
  t.references :communication_method, :polymorphic => true
end

class Notification < ActiveRecord::Base
  belongs_to :communication_method, :polymorphic => true
  belongs_to :email_address, foreign_key: 'communication_method_id'
  belongs_to :phone_number, foreign_key: 'communication_method_id'
end

module CommunicationMethod
  def self.included(base)
    base.instance_eval do
      has_many :notifications, :as => :communication_method, :inverse_of => :communication_method, :dependent => :destroy
    end
  end
end

class EmailAddress
  include CommunicationMethod
end

class PhoneNumber
  include CommunicationMethod
end

now I want to have more than one communication method per notifications, is it possible? (something like has_many :communication_methods, :polymorphic => true ) I guess I will also need a migration in oder to create a many to many table of notifications to communication methods

Answer 1

As I know Rails still have no support for polymorphic has_many associations. I was solving this adding new intermediate model, which has polymorphic association. For your case it can be like the following:

class Notification < ActiveRecord::Base
  has_many :communication_method_links
  has_many :email_communication_methods, :through => :communication_method_links, :class_name => 'EmailAddress'
  has_many :email_communication_methods, :through => :communication_method_links, :class_name => 'PhoneNumber'
  belongs_to :email_address, foreign_key: 'communication_method_id'
  belongs_to :phone_number, foreign_key: 'communication_method_id'
end

class CommunicationMethodLink < ActiveRecord::Base
  belongs_to :notification
  belongs_to :communication_methods, :polymorphic => true
end

module CommunicationMethod
  def self.included(base)
    base.instance_eval do
      has_many :communication_method_links, :as => :communication_method, :inverse_of => :communication_method, :dependent => :destroy
    end
  end
end

class EmailAddress
  include CommunicationMethod
end

class PhoneNumber
  include CommunicationMethod
end

So the migration for CommunicationMethodLink will look like this:

create_table :communication_method_links do |t|
  t.references :notification
  t.references :communication_method, :polymorphic => true
end