Many to one relation


#1

-i searched through the news group but couldn’t find the answer for my
problem.
example:

----------- classes ----------
class Car < ActiveRecord::Base
has_one :colour
def after_create()
colour = Colour.new
colour.name = ‘colour1’
colour.save
end
end

class Chair < ActiveRecord::Base
has_one :colour
end

class Colour < ActiveRecord::Base
end
-------------- tables ---------
create table cars(id int PRIMARY KEY NOT NULL AUTO_INCREMENT,name
varchar(50),colour_id int NOT NULL, primary key(id));

create table chairs(id int PRIMARY KEY NOT NULL AUTO_INCREMENT,name
varchar(50),colour_id int NOT NULL);

create table colours(id int PRIMARY KEY NOT NULL AUTO_INCREMENT,name
varchar(50));

  • i consider it a many to one relation because diferent types of items
    are refering to one type (Car and Chair both have colour).
  • i wrote the models as above i create a Car object, i save it but
    alwayes my colour_id in the database remains 0.
    I would appreciate if your could give me a hint.

#2

When you say “car has one colour”, the other side of the relationship
must
read “colour belongs to car”. Now the entity that has the belongs to
relationship is the one which will have the foreign key, in this case it
will be car_id.

So, your tables must define the foreign keys prperly and also declare
the
belongs to relationship. Make the changes and run again and see if the
record gets populated.