How to set up custom string foreign key in Rails 4?

Question

How to set up associations to set up properly has_one using string foreign_key?

class Pharmaceutic < ActiveRecord::Base
  has_one :pharmaceutic_group, foreign_key: "code"
end

class PharmaceuticGroup < ActiveRecord::Base
  belongs_to :pharmaceutic, primary_key: 'code'
end

>> Pharmaceutic.last.pharmaceutic_group                                                                                        
  Pharmaceutic Load (0.3ms)  SELECT `pharmaceutics`.* FROM `pharmaceutics` ORDER BY `pharmaceutics`.`id` DESC LIMIT 1
  PharmaceuticGroup Load (0.3ms)  SELECT `pharmaceutic_groups`.* FROM `pharmaceutic_groups` WHERE `pharmaceutic_groups`.`code` = 2 ORDER BY `pharmaceutic_groups`.`id` ASC LIMIT 1
=> nil
>> Pharmaceutic
=> Pharmaceutic(id: integer, package_type: integer, group_code: string)
>> PharmaceuticGroup
=> PharmaceuticGroup(id: integer, code: string, name: string)

For example when: Pharmaceutic has group_code: aaa and PharmaceuticGroup has code: aaa I would like to get Pharmaceutic.last.pharmaceutic_group.name => 'AAA group name'

Answer 1

I guess you should rather use Pharmaceutic belongs_to :pharmaceutic_group and PharmaceuticGroup has_many :pharmaceutics, like this:

class Pharmaceutic < ActiveRecord::Base
  belongs_to :pharmaceutic_group, foreign_key: :group_code, primary_key: :code
end

class PharmaceuticGroup < ActiveRecord::Base
  has_many :pharmaceutics, foreign_key: :group_code, primary_key: :code
end