这种关系可以在 Ruby on Rails 中描述吗？

Question

这种关系可以在 Ruby on Rails 的 ActiveRecord 模型关系中描述吗？

   Customer                          Address
   ===================               =========
   Billing_Address_Id  >------}
                              }---|- AddressId
   Shipping_Address_Id >------}

这样我就可以获得如下所示的数据：

地址：

   Id | Addr           | City     | State | Zip   |
   ================================================
   1  | 123 Main       | New York | NY    | 99999 |
   2  | 200 2nd Street | New York | NY    | 99999 |
   3  | 300 3rd Street | Albany   | NY    | 99998 |
   4  | PO Box 4       | Albany   | NY    | 99998 |

客户：

   Id | Name | Billing_Address_Id | Shipping_Address_Id  |
   =======================================================
   1  | Bob  | 1                  | 1                    |
   2  | Al   | 2                  | 1                    |
   3  | Joe  | 3                  | 4                    |

我想将地址存储在他们自己的表中，因为数据可能会在客户之间共享（尤其是送货地址）。但是对于任何给定的客户，甚至只有两个地址。

除非没有其他办法，否则我想避免多对多关系。

Answer 1

是的，完全有可能做到这一点。给定一个 customers 表，其中有两个外键 shipping_address_id 和 billing_address_id 到 addresses 表，您的 Customer 模型可能如下所示：

class Customer < ActiveRecord::Base
  belongs_to :billing_address, :class_name => 'Address'
  belongs_to :shipping_address, :class_name => 'Address'
end

这将让客户为送货地址和帐单地址引用相同的地址行，并且还可以让多个客户共享地址。

更新：在分享对此类地址的引用时，您可能需要仔细考虑如何处理地址更新。在您的示例中，Bob 和 Al 共享相同的送货地址。现在，如果 Bob 更新了他的送货地址，您可能想要为 Bob 的新地址创建一个新的 Address 记录，而不是更新现有记录，以避免也更改 Al 的地址。有时，您实际上可能希望在这种情况下更新两个客户的地址，但在大多数情况下您可能不会。

Answer 2

给定这样的表定义：

create_table :addresses do |t|
  t.string :street
  t.string :city
  t.string :state
  t.string :zip
  t.timestamps
end

create_table :customers do |t|
  t.string     :name
  t.references :shipping_address
  t.references :billing_address
  t.timestamps
end

您可以将帐单和送货地址与您的客户相关联，如下所示：

class Customer < ActiveRecord::Base
  belongs_to :shipping_address, :class_name => "Address"
  belongs_to :billing_address,  :class_name => "Address"
end

Answer 3

The documentation for ActiveRecord associations has a section on has_one vs belongs_to. 此外，section on has_one 提到仅当 other 类 具有外键时才应使用它。因此，要对您想要的模型进行建模，您可以使用。

class Address < ActiveRecord::Base
  has_one :shipto_customer, :class_name => "Customer", :foreign_key => "shipping_address_id"
  has_one :billto_customer, :class_name => "Customer", :foreign_key => "billing_address_id"
end

class Customer < ActiveRecord::Base
  belongs_to :shipping_address, :class_name => "Address"
  belongs_to :billing_address,  :class_name => "Address"
end

示例用法：

>> customer = Customer.new(:name => "John Smith",
?>     :shipping_address => Address.new(:address => "123 M St",
?>       :city => "Phoenix", :state => "AZ", :zip => "85015"),
?>     :billing_address => Address.new(:address => "555 W Main Dr",
?>       :city => "Phoenix", :state => "AZ", :zip => "85015")
>>   )
=> #<Customer id: nil, name: "John Smith", billing_address_id: nil, shipping_address_id: nil, created_at: nil, updated_at: nil>
>> customer.save
  Address Create (0.8ms)   INSERT INTO "addresses" ("address", "city", "zip", "created_at", "updated_at", "state") VALUES('555 W Main Dr', 'Phoenix', '85015', '2009-11-14 17:03:28', '2009-11-14 17:03:28', 'AZ')
  Address Create (0.2ms)   INSERT INTO "addresses" ("address", "city", "zip", "created_at", "updated_at", "state") VALUES('123 M St', 'Phoenix', '85015', '2009-11-14 17:03:28', '2009-11-14 17:03:28', 'AZ')
  Customer Create (0.2ms)   INSERT INTO "customers" ("name", "billing_address_id", "shipping_address_id", "created_at", "updated_at") VALUES('John Smith', 1, 2, '2009-11-14 17:03:28', '2009-11-14 17:03:28')
=> true
>> customer.shipping_address
=> #<Address id: 2, address: "123 M St", city: "Phoenix", state: "AZ", zip: "85015", created_at: "2009-11-14 17:03:28", updated_at: "2009-11-14 17:03:28">
>> customer.billing_address
=> #<Address id: 1, address: "555 W Main Dr", city: "Phoenix", state: "AZ", zip: "85015", created_at: "2009-11-14 17:03:28", updated_at: "2009-11-14 17:03:28">
>>