Rails的协会通过多层次 [英] Rails Associations Through Multiple Levels

问题描述

我是比较新的Rails和我的工作有关，涉及到数据的多个嵌套级别的项目。我有做适当的关联，以便我能得到一个模型3个级别更高的所有子元素的问题。这里是模型的一个示例：

I am relatively new to Rails and am working on a project that involves multiple, "nested" levels of data. I am having issues making the proper associations so I can get all the child elements of a model 3 levels higher. Here is an example of the models:

class Country < ActiveRecord::Base
  has_many :states
end

class State < ActiveRecord::Base
  belongs_to :country
  has_many :cities
end

class City < ActiveRecord::Base
  belongs_to :state
  has_many :people
end

class Person < ActiveRecord::Base
  belongs_to :city
end

我已经实现了国家模式，的has_many的关系：城市：通过=＆GT; ：美国并试图调用 Country.first.cities.all ，其工作方式。不过，我在访问所有的人在特定的国家，当我尝试的问题 Country.first.cities.all.people.all 在人物控制器。

I have implemented a relationship in the Country model, has_many :cities, :through => :states and have tried to call Country.first.cities.all, which works. However, I am having issues accessing all the people in a given country when I try Country.first.cities.all.people.all in the People controller.

什么是处理这种情况的关联的最好方法？我要补充一个外键给每个孩子表，如 COUNTRY_ID ，让我可以得到所有的人在国家？任何建议将是AP preciated。

What is the best way to deal with this sort of association situation? Should I add a foreign key to each of the children tables, such as country_id, so that I can get all the People in a Country? Any suggestions would be appreciated.

推荐答案

的原因在于Country.first.cities.all是一个数组，并且每个这元件具有方法的人，而不是城市的整个集合。你会发现，这个作品：

The reason is that Country.first.cities.all is an array, and each of it's elements has the method people, instead of the entire collection of cities. You'll notice that this works:

Country.first.cities.first.people.all

由于第一个国家的第一个城市拥有人的方法。为了得到一个国家的所有的人的名单，你可以做一个单一查询以下内容：

Because the first city of the first country has the people method. To get a list of all people in a country, you could do the following in a single query:

People.joins(:city => {:state => :country})
  .where(:country => {:id => Country.first.id}).all

这篇关于Rails的协会通过多层次的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！