Question

我有一个应用程序，其中数据库表things包含locatable个对象 - 如城市，地址，聚会场所，公交车站等。

一个可定位的对象可以例如成为一个城市和国家。这些对象通过多态has_one关联连接到Thing，因为每个City代表一个可定位的Thing。但是国家也has_many :cities，因为所有国家都位于特定国家。我正在使用这种结构做各种奇怪的关联请求，到目前为止（使用Rails 3.0）它运行良好。但是使用Rails 4.2，它失败了，见下文。

这是数据库结构：

  Thing: id, locateable_id, locateable_type, lat, lng, name, country_id, city_id, ...
   City: id, name, country_id
Country: id, name

代码：

class Thing < AR::Base
  belongs_to :locateable, :polymorphic => true
  belongs_to :country
  belongs_to :city
  ...
end

class Country < AR::Base
  has_one :thing, as: :locatable
  has_many :cities
  ...
end

class City < AR::Base
  has_one :thing, as: :locatable
  ...
end

在Rails 3.0.20，Ruby 1.9.3中，调用此代码

1.9.3-p551 :005 > Thing.find_by_name("Aachen").country.thing
# Thing Load (0.5ms)  SELECT "things".* FROM "things" WHERE "things"."name" = 'Aachen' LIMIT 1
# Country Load (0.3ms)  SELECT "countries".* FROM "countries" WHERE "countries"."id" = 276 ORDER BY name LIMIT 1
# Thing Load (0.3ms)  SELECT "things".* FROM "things" WHERE ("things".locateable_id = 276 AND "things".locateable_type = 'Country') LIMIT 1
=> <Thing id: 355371, locateable_id: 276, locateable_type: "Country", name: "Deutschland", country_id: 276, ...>

将返回这个城市的国家。在Rails 4.2.5，Ruby 2.2.1中，完全相同的代码再次返回城市的事物：

2.2.1 :008 >  Thing.find_by_name("Aachen").country.thing
# Thing Load (0.4ms)  SELECT  "things".* FROM "things" WHERE "things"."name" = $1 LIMIT 1  [["name", "Aachen"]]
# Country Load (0.3ms)  SELECT  "countries".* FROM "countries" WHERE "countries"."id" = $1  ORDER BY name LIMIT 1  [["id", 276]]
=> <Thing id: 105548, locateable_id: 3, locateable_type: "City", name: "Aachen", country_id: 276, city_id: 3, ...>

为什么呢？这似乎不正确。特别是因为它不一致：

> Country.find(276).thing
=> #<Thing id: 355371, locateable_id: 276, locateable_type: "Country", coordinate_id: nil, name: "Deutschland", ...>
# but
> c = Thing.find_by_name("Aachen").country
=> <Country id: 276, name: "Deutschland">
> c.thing
=> #<Thing id: 105548, locateable_id: 3, locateable_type: "City", coordinate_id: nil, name: "Aachen", ...>

这可能是Rails中的一个错误吗？或者我是否滥用多态关联系统？

Rails 4.2.5：Polymorphic has_one关联指向同一个对象

0 个答案: