Rails has_many / belong_to协会

Question

With has_many belongs_to or any of the associations:

1. Does it matter which object of the two models is created first?
2. Is there a convention, as to which should be created first?

Answer 1

No, it does not matter which one is created first as Rails will solve the correct order for you.

In case of a belongs_to / has_one association

class Parent < ActiveRecord::Base
  has_many :children
end

class Children < ActiveRecord::Base
  belongs_to :parent
end

p = Parent.new(name: 'Jhon')
p.children << Children.new
p.save
(0.3ms)  BEGIN
 SQL (27.1ms)  INSERT INTO `parents` (`name`) VALUES ('Jhon')
 SQL (23.1ms)  INSERT INTO `childrens` (`parent_id`) VALUES (7842)
(95.0ms)  COMMIT

Answer 2

The relationships are set up in the models, after the tables are created. Therefore, it doesn't matter which order your create the actual tables.

I typically will create the more dominate of the two first, such as create User, and then any relations after. But again, there isn't any reason to have an order to create them.

Answer 3

You're talking about one to many relationship.

Parent has_many Children and Child belongs_to Parent