Ruby on Rails Getting Foreign Key to work

March 5, 2023

I feel like this is a simple error that I can not figure out, but I haven’t found anything online to help explain what I am doing incorrectly. I have three tables created in my Ruby on Rails application:

Facility
 facility_name - string
 address       - string
 city_id       - integer
 state_id      - integer
 
 and foreign keys: cities, states

City
  city_name    - integer
  state_id     - integer

State
  state_short  - string
  state_long   - string

and I have the models defined as:

class Facility < ApplicationRecord
  has_one :city
  has_one :state
end


class City < ApplicationRecord
  belongs_to :state
  belongs_to :facility
end

class State < ApplicationRecord
  has_many :cities
  belongs_to :facility
end

I thought I would be able to bring up the city and state within the facility by the following code on the rails console:

x = Facility.first
x.city_name
x.state_long

but both of those codes give an error. Am I mistaking that by having the city_id and the state_id in the facilities table and the relationships as above, I should be able to get the city_name and state_long from the respective tables?

>Solution :

class Facility < ApplicationRecord
  has_one :city
  has_one :state
end

It means cities and states tables have facility_id column

But in your schema facilties have city_id and state_id

It means you need change your associations this way

class Facility < ApplicationRecord
  belongs_to :city
  belongs_to :state
end

class City < ApplicationRecord
  belongs_to :state
  has_one :facility
end

class State < ApplicationRecord
  has_many :cities
  has_one :facility
end

Another option is to change schema (if keep associations)

facilities
-----------
facility_name
address

cities
-----------
city_name
state_id 
facility_id

states
-----------
state_short
state_long
facility_id

Other words you need choose between belongs_to and has_one

The distinction is in where you place the foreign key (it goes on the table for the class declaring the belongs_to association), but you should give some thought to the actual meaning of the data as well. The has_one relationship says that one of something is yours – that is, that something points back to you