Question

I am working on a Rail webapp. I have two models, User, which contains very basic information: id, username and password, and Profile, which includes profile for each user. (The main reason is to have a lightweight User model, which will be called regularly, and a full-fledged profile which will be called irregularly). Each of these models has many children.

Right now, I have Profile with its own primary key, then a foreign key user_id to match with User.

However, I wonder if I should have Profile model with the same key as User model (i.e., Profile.id == User.id if the records refer to the same user). This is convenience because when I have an object that belongs to User, I want it to belong to Profile and vise versa. For example, I can specify User has_many and Spec has_many relationship to ChildModel. Because they use the same key, I don’t have to merge ChildModel to Spec, then Profile to User to find out user associated with child object.

The downside is in the future, if for some reason I have discrepancy between primary key of User and Spec, then I am in deep trouble.

What would be your recommendation for this situation?

Thank you.

Answer 1

It sounds like you should be using a one-to-one relationship between Profile and User. You can create this using the has_one and belongs_to declarations.

class User < ActiveRecord::Base
  has_one :profile
end

class Profile < ActiveRecord::Base
  belongs_to :user
end

As stated in Agile Web Development with Rails Fourth Edition:

There’s an important rule illustrated here: the model for the table that contains the foreign key always has the belongs_to declaration.