Adding attributes to a join model during assignment to parent model - sql

Question

I have the following setup:
Schema.rb
ActiveRecord::Schema.define(version: 20130923235150) do
create_table "addresses", force: true do |t|
t.datetime "created_at"
t.datetime "updated_at"
end
create_table "user_addresses", force: true do |t|
t.integer "user_id"
t.integer "address_id"
t.string "purpose"
t.datetime "created_at"
t.datetime "updated_at"
end
create_table "users", force: true do |t|
t.datetime "created_at"
t.datetime "updated_at"
end
end
User.rb:
class User < ActiveRecord::Base
has_one :user_address
has_one :primary_shipping_address, through: :user_address, class_name: :UserAddress, source: :address
has_one :primary_billing_address, through: :user_address, class_name: :UserAddress, source: :address
end
Address.rb:
class Address < ActiveRecord::Base
has_one :user_address
has_one :primary_shipping_user, through: :user_address, class_name: :UserAddress, source: :user
has_one :primary_billing_user, through: :user_address, class_name: :UserAddress, source: :user
end
UserAddress.rb:
class UserAddress < ActiveRecord::Base
belongs_to :user
belongs_to :address
end
When someone does user.primary_billing_address = address, I want the join model instance to have "billing" set as its purpose. Similarly with shipping and "shipping". Ex.
irb(main):013:0> u = User.new
=> #<User id: nil, created_at: nil, updated_at: nil>
irb(main):014:0> a = Address.create
=> #<Address id: 3, created_at: "2013-09-24 00:13:07", updated_at: "2013-09-24 00:13:07">
irb(main):015:0> u.primary_billing_address = a
=> #<Address id: 3, created_at: "2013-09-24 00:13:07", updated_at: "2013-09-24 00:13:07">
irb(main):016:0> u.save!
=> true
irb(main):017:0> u.user_address
=> #<UserAddress id: 2, user_id: 3, address_id: 3, purpose: nil, created_at: "2013-09-24 00:13:18", updated_at: "2013-09-24 00:13:18">
(not what I want... purpose should be "billing")
How can I do this such that it works for new AND persisted records?. I've come up with solutions that are 90% there, but break on some random spec due to an edge case my approach didn't catch.
The trickiest part to work around is how association= behaves: on new records, it queues the association for assignment through the join model.
PS: I left out the conditionals on the has_one relationships that I'd use to get the address I want. I think this issue is independent of that.

Answer 1

First, the associations are a bit off, both primary_shipping_address and primary_billing_address will return same address. You can change it to
class User < ActiveRecord::Base
has_many :user_addresses # user can have multiple addresses one for shipping and one for billing
has_one :primary_shipping_address,
through: :user_address, class_name: :UserAddress,
source: :address, :conditions => ['user_addresses.purpose = ?','shipping']
has_one :primary_billing_address,
through: :user_address, class_name: :UserAddress,
source: :address, :conditions => ['user_addresses.purpose = ?','billing']
end
To save the purpose while saving the address, there are two options.
Option 1 : Override the default association= method
# alias is needed to refer to original method
alias_method :orig_primary_billing_address=, :primary_billing_address=
def primary_billing_address=(obj)
self.orig_primary_billing_address = obj
self.user_addresses.where("address_id = ?", obj.id).update_attribute(:purpose, 'billing')
end
# repeat for shipping
Option 2 : Create a custom method (I prefer this as it is cleaner and DRY)
def save_address_with_purpose(obj,purpose)
self.send("primary_#{purpose}_address=", obj)
self.user_addresses.where("address_id = ?", obj.id).update_attribute(:purpose, purpose)
end