How do I add migration with multiple references to the same model in one table? Ruby/Rails

Question

How do I create a migration with two fields that reference the same table? I have tables A, and image. A.image1_id will reference image, and A.image2_id will reference image

Answer 1

You can do this simply with the add_column method in your migrations and set up the proper associations in your classes:

class AddFields < ActiveRecord::Migration
  def change
    add_column :tickets, :image_1_id, :integer
    add_column :tickets, :image_2_id, :integer
  end
end

class Ticket < ActiveRecord::Base
  belongs_to :image_1, :class_name => "Image"
  belongs_to :image_2, :class_name => "Image"
end

class Image < ActiveRecord::Base
  has_many :primary_tickets, :class_name => "Ticket", :foreign_key => "image_1_id"
  has_many :secondary_tickets, :class_name => "Ticket", :foreign_key => "image_2_id"
end

This blog post, Creating Multiple Associations with the Same Table, goes into more detail.

Answer 2

In Rails 5.1 or greater you can do it like this:

Migration

class AddFields < ActiveRecord::Migration
   def change
    change_table(:tickets) do |t|
        t.references :image1, foreign_key: { to_table: 'images' }
        t.references :image2, foreign_key: { to_table: 'images' }
    end
  end
end

This will create the fields image1_id, and image2_id and make the database level references to the images table

Models

as in rossta's asnwer

class Ticket < ActiveRecord::Base
  belongs_to :image_1, class_name: "Image"
  belongs_to :image_2, class_name: "Image"
end

class Image < ActiveRecord::Base
  has_many :primary_tickets, class_name: "Ticket", foreign_key: "image_1_id"
  has_many :secondary_tickets, class_name: "Ticket", foreign_key: "image_2_id"
end

FactoryBot

If you uses FactoryBot then your factory might look something like this:

FactoryBot.define do
  factory :ticket do
    association :image1, factory: :image
    association :image2, factory: :image
  end
end