ActiveRecord: Do I need both belongs_to and has_one

Question

I have 2 models, namely user and userprofile. There is a one-to-one relationship between user and userprofile.

Answer 1

You define the association wherever you will need it. If at some point you need to say user.userprofile, then include has_one :userprofile in User. Likewise, if you need to say userprofile.user, then include belongs_to user in Userprofile.

In other words, associations are relative. You can specify that model A has_one :b without specifying that model B belongs_to :a. You simply define what you need. The same goes for one-to-many and many-to-many associations.

Just be sure to have migrated user_id to the "userprofiles" table.

Answer 2

Having just a belongs_to relationship between userprofiles and user does default to has_one. However, it would be wise (Rails-proper) to specify the association on both models.

After all, if you wanted a has_many association (etc) you would want to specify that.

Check out http://guides.rubyonrails.org/association_basics.html for more info