Rails 4 Secondary ID For Users With STI

Question

In a Rails 4 App users can be of 2 different types, regular or premium, stored with PostgreSQL, using Single Table Inheritance because they have very similar attributes.

When a user (regular) signs up to premium, I would like to be able to keep track of his ":premium_user_id" which would basically be a second :id column in the user table:

• If user with :id 25 is the first user to sign up to premium, his :premium_user_id is 1
• If user with :id 57 is the second user to sign up to premium, his :premium_user_id is 2

and so on.

I could add a :premium_user_id column in the User table with an index, and in the premium sign up action call increment that id like so:

current_user.update_attribute :premium_user_id, User.maximum("premium_user_id") + 1

I am not so sure about the fact that this solution needs a DB call each time, but I can't think of a place to store that Max Premium Id to avoid the db call.

Any idea for a better way to implement this?

In particular by implementing this on the Database Level through migrations and SQL statements.

Thank you for your suggestions.

Answer 1

Add migration

def up
  add_column :users, :premium_user_id, :integer
  execute <<-SQL
    CREATE SEQUENCE premium_user_id_seq START 1;
    ALTER SEQUENCE premium_user_id_seq OWNED BY users.premium_user_id;
    ALTER TABLE users ALTER COLUMN premium_user_id SET DEFAULT nextval('premium_user_id_seq');
  SQL
end


def down
  remove_column :users, :premium_user_id
  execute <<-SQL
    DROP SEQUENCE premium_user_id_seq;
  SQL
end

Add callback

class User < ActiveRecord::Base
  after_commit do
    unless read_attribute(:type) == 'premium'
      update_column :premium_user_id, nil
    end
  end
end