Sql 在分配给父模型期间向联接模型添加属性

我有以下设置：

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

如何才能使其适用于新的和持久化记录？。我已经提出了90%的解决方案，但由于我的方法没有抓住一个边缘案例，在一些随机规范上出现了突破

要解决的最棘手的部分是

关联=

的行为：在新记录上，它通过联接模型将关联排队等待分配

---

注：我省略了

has_one

关系上的条件，我将使用这些关系来获取我想要的地址。我认为这个问题与此无关。

首先，关联有点不一致，

primary\u shipping\u address

和

primary\u billing\u address

将返回相同的地址。你可以把它改成

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

选项2：创建自定义方法（我更喜欢这种方法，因为它更干净干燥）

---

我想您需要定义一个before_save方法来检查账单地址的设置，并适当地设置目的？我如何知道要分配哪个目的？

class UserAddress < ActiveRecord::Base
  belongs_to :user
  belongs_to :address
end

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")

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

   # 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

   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