Question

I’ve got the an has_one association:

has_one association user -> customer models

will the user have the customer_id or customer will have the user_id attribute?

other question: into my _form i’d like to have a select/option with all the users that hasn’t associated with a customer which is the best way to do that?

thanks a lot.

Answer 1

The _id field is always in the model with the belongs_to, and refers to the other table name.

class Customer < ActiveRecord::Base
  belongs_to :user
end

class User < ActiveRecord::Base
  has_one :customer
end

In this case, the customers table will have a user_id field.

For the second question, missing values are found in SQL using outer joins.
The SQL you want would be

select 
from users
  left outer join customers on users.id = customers.user_id
where customers.id is null

In ActiveRecord, add a scope to your User class.

In Rails 3.x:

class User < ActiveRecord::Base
  has_one :customer

  scope :missing_customer,
    includes(:customer).where("customers.id is null")
end

In Rails 2.3.x:

class User < ActiveRecord::Base
  named_scope :missing_customer,
    { :joins => "left outer join customers on users.id = customers.user_id",
      :conditions => "customers.id is null" }
end