多态关联ID，has_one和唯一性

Question

I have a polymorphic association, where an Admin and a Developer each have a User (for a common authentication mechanism)

Developer.rb

class Developer < ActiveRecord::Base
  attr_accessible :skype_name
  has_one :user, :as => :profile, :dependent => :destroy
  accepts_nested_attributes_for :user
end

Admin.rb is identical but doesn't add any new attributes

User.rb

class User < ActiveRecord::Base
  attr_accessible :email, :name, :password, :password_confirmation, :profile_id, :profile_type
  has_secure_password

  belongs_to :profile, :polymorphic => true
  before_save { |user| user.email = email.downcase }

  ... some validations for unique email and before_save stuff ...
end

When I create Developers or Admins via the rails console, User.profile_id is always unique, and it is the same as the Developer or Admin I've just created. It also seems to match with the diagram here

If I have a User with profile_type = Developer , and I want to get a reference to the Developer, is it safe to get the reference by calling Developer.find(u.profile_id) , and similarly for Admins? And if not, then how can I do it safely?

It works at the moment, but I'm not sure if it's just lucky because my tables are small.

Answer 1

Yes. The quick answer is that because you set the profile type to "Developer", the User profile id should match the one in the Developer table. Imagine for a second that you have

User One

id: 1
name: Bob
profile_type: Developer
profile_id: 1

User Two

id: 2
name: Shelly
profile_type: Admin
profile_id: 1

Because you set up the polymorphic association, Rails handles all the work for you. No need to worry about id conflicts. Unless of course you change User Two to

Updated User Two

id: 2
name: Shelly
profile_type: Developer
profile_id: 1

Then Rails won't know what to do when you have two user's as the same developer.

And within your Developer and Admin's table you should find

Developers Table

id: 1
skype_name Bob123

Admin's Table

id: 1
skype_name Shelly78