Hi,
suppose I'm doing a rails system for the DMV.
The rules say:
A person may have 0 or 1 Drivers License.
So, I'd have these 2 tables:
class CreatePeople < ActiveRecord::Migration def self.up create_table :people do |t| t.column :name, :string end end
def self.down drop_table :people end end
class CreateDriverslicenses < ActiveRecord::Migration def self.up create_table :driverslicenses do |t| t.column :person_id, :integer end end
def self.down drop_table :driverslicenses end end
And these models:
class Person < ActiveRecord::Base has_one :driverslicense end
class DriversLicense < ActiveRecord::Base belongs_to :person end
What is the best way to enforce this rule:
A person may have 0 or 1 Drivers License. ??
I ran a simple test with console:
pete = Person.new
=> #<Person:0x2364d9c @attributes={"name"=>nil}, @new_record=true>
pete.name = 'Pete'
=> "Pete"
dl1 = Driverslicense.new
=> #<Driverslicense:0x235ac0c @attributes={"person_id"=>nil}, @new_record=true>
dl1.person_id = pete
=> #<Person:0x2364d9c @errors=#<ActiveRecord::Errors:0x23511ac @errors={}, @base=#<Person:0x2364d9c ...>>, @attributes={"name"=>"Pete", "id"=>1}, @new_record=false>
dl1.person.name
=> "Pete"
So, now Pete has a drivers license.
Let's try to give him another drivers license:
dl2 = Driverslicense.new
=> #<Driverslicense:0x233de2c @attributes={"person_id"=>nil}, @new_record=true>
dl2.person_id = pete
=> #<Person:0x2364d9c @errors=#<ActiveRecord::Errors:0x23511ac @errors={}, @base=#<Person:0x2364d9c ...>>, @attributes={"name"=>"Pete", "id"=>1}, @new_record=false>
dl2.person.name
=> "Pete"
It appears that dmv has assigned 2 drivers licenses to Pete.
Is it up to me to 'strengthen' the has_one() method in AR?
Here is info about my rails:
$ script/about About your application's environment Ruby version 1.8.4 (powerpc-darwin7.9.0) RubyGems version 0.9.0 Rails version 1.1.6 Active Record version 1.14.4 Action Pack version 1.12.5 Action Web Service version 1.1.6 Action Mailer version 1.2.5 Active Support version 1.3.1
-Pete http://GoodJobFastCar.com goodjobfastcar@gmail.com
