Ruby on Rails ActiveRecord: table with foreign keys in more than one other table

Question

I'm new to Ruby on Rails and I'm trying to model my table relationships.

To simplify the problem, let's say I have 3 tables:
-- Customer (id, address_id, ...)
-- Employee (id, address_id, ...)
-- Address (id, ...)

Would the Address model have the following?

has_one :customer
has_one :employee

I know this is true in the case of a single relationship, but I couldn't find any examples where there were two "has_one" relationships like that.

Answer 1

You should use polymorphic associations as shown below.

# Address model
class Address < ActiveRecord::Base
  belongs_to :addressable, :polymorphic => true
end

# Customer model
class Customer < ActiveRecord::Base
  has_one :address, :as => :addressable
end

# Employee model
class Employee < ActiveRecord::Base
  has_one :address, :as => :addressable
end

# Migration script for `addresses` table
class CreateAddresses < ActiveRecord::Migration
  def self.up
    create_table :addresses, :force => true do |t|
      t.references :addressable, :polymorphic => true, :null => false

      # add other address fields

      t.timestamps      
    end

    add_index :addresses, ["addressable_id", "addressable_type"], :name => "fk_addressable"

end

Now you can do the following:

customer = Customer.new
customer.address = Address.new(:street => "ABC", :city => "SF", :zip => "46646")
customer.save

OR

employee = Employee.last
print employee.address.street