如何在Rails中两次加入相同的2个模型? [英] How can I join the same 2 models twice in Rails?

问题描述

我有一个具有国家/地区偏好设置的应用程序.用户将具有两种国家/地区偏好设置-事件和研究.将来可能还会更多.我更倾向于使用2个表来表示这一点，而不是使用STI.我在优雅地配置Rails时遇到了一些麻烦.我可以破解它，但是我更愿意按照Rails的惯例来做到这一点.我想要的是这样的:

I have an app with country preferences. A user will have 2 types of country preferences - event and research. In the future there may be more. I was leaning more towards having 2 tables to represent this over using STI. I'm having a bit of trouble configuring Rails elegantly to do this. I could hack it but I would rather do this by Rails convention. What I want is something like this:

class User < ActiveRecord::Base
  has_many event_countries, :through => :event_countries, :class_name => 'Country'
  has_many research_countries, :through => :research_countries, :class_name => 'Country'
end

class EventCountry < ActiveRecord::Base
  belongs_to :country
  belongs_to :user
end

class ResearchCountry < ActiveRecord::Base
  belongs_to :country
  belongs_to :user
end

class Country < ActiveRecord::Base
...
end

这是行不通的.有了这个伪代码"，没有人知道如何在Rails中实际实现吗?

This doesn't work though. Given this "pseudo code" does anyone know how to actually implement this in Rails?

推荐答案

我认为您要声明它们错误，因为这应该可以正常工作.这就是:through指令的用途:

I think you're going about declaring them wrong, because this should work properly. That's what the :through directive is for:

class User < ActiveRecord::Base
  has_many :event_countries
  has_many :countries_with_events,
    :through => :event_countries,
    :source => :country

  has_many :research_countries
  has_many :countries_with_researches,
    :through => :research_countries,
    :source => :country
end

class EventCountry < ActiveRecord::Base
  belongs_to :country
  belongs_to :user
end

class ResearchCountry < ActiveRecord::Base
  belongs_to :country
  belongs_to :user
end

class Country < ActiveRecord::Base
  # ...
end

很多尴尬都来自您为表格选择的标签.尽管乍一看它们似乎很合理，但是使用它们的方式最终使它们变得困难.

A lot of the awkwardness comes from the labels you've chosen for the tables. Although they'd seem reasonable at first glance, the way you use them ends up making them difficult.

您可能想调用research_countries之类的user_research_countries，以便关系名称可以作为user.research_countries作为:through:

You might want to call research_countries something like user_research_countries so that the relationship name can be user.research_countries as the :through:

class User < ActiveRecord::Base
  has_many :user_event_countries
  has_many :event_countries,
    :through => :user_event_countries,
    :source => :country

  has_many :user_research_countries
  has_many :research_countries,
    :through => :user_research_countries,
    :source => :country
end

class UserEventCountry < ActiveRecord::Base
  belongs_to :country
  belongs_to :user
end

class UserResearchCountry < ActiveRecord::Base
  belongs_to :country
  belongs_to :user
end

class Country < ActiveRecord::Base
  # ...
end

您可以通过在用户国家/地区关联表中添加一个包含一个或多个标志的字段来进一步重构该字段，在这种情况下，这将是研究或事件，或者以后您需要执行的任何操作:

You can refactor this even further by adding a field to the user-country association table that includes one or more flags, which in this case would be research or event or whatever you require later:

class User < ActiveRecord::Base
  has_many :user_countries
  has_many :event_countries,
    :through => :user_countries,
    :source => :country,
    :conditions => { :event => true }
  has_many :research_countries,
    :through => :user_countries,
    :source => :country,
    :conditions => { :research => true }
end

class UserCountry < ActiveRecord::Base
  belongs_to :country
  belongs_to :user

  # * column :event, :boolean
  # * column :research, :boolean
end

class Country < ActiveRecord::Base
  # ...
end

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