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如何在Rails中加入相同的2个模型两次?

has-and-belongs-to-many ruby-on-rails

Tony · 技术社区 · 15 年前

我有一个具有国家偏好的应用程序。用户将有两种国家偏好-活动和研究。将来可能会有更多。我更倾向于用两张桌子来代表这个,而不是用STI。我很难优雅地配置Rails来完成这项工作。我可以破解它,但我宁愿通过Rails约定来实现。我想要这样的东西:

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

但这不起作用。考虑到这个“伪代码”,有人知道如何在Rails中实际实现它吗?

1 回复 | 直到 15 年前

tadman 15 年前

我认为你要宣布他们错了,因为这应该是正确的。这就是 :through 指令用于:

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

很多尴尬来自于你为桌子选择的标签。虽然乍一看它们似乎是合理的,但你使用它们的方式最终使它们变得困难。

你可能想打电话 research_countries 有点像 user_research_countries 以便关系名称可以是 user.research_countries 作为 :到 :

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

您可以通过向用户国家/地区关联表中添加包含一个或多个标志的字段来进一步重构这一点,在这种情况下,这些标志将是研究或事件,或者稍后需要的任何内容:

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