Question

我有以下四种模式：

#models/team.rb
class Team < ActiveRecord::Base
  has_many :locations
end

#models/location.rb
class Location < ActiveRecord::Base
  belongs_to :team
  has_many :relationships
  has_many :contacts, through: :relationships
end

#models/relationship.rb
class Relationship < ActiveRecord::Base
  belongs_to :location
  belongs_to :contact
end

#models/contact.rb
class Contact < ActiveRecord::Base
  has_many :relationships
  has_many :locations, through: :relationships
end

我想在Team模型上设置一个方法，我可以调用该方法来抓取该团队的所有关联contacts。例如：

team = Team.find 1
this_teams_contacts = team.contacts

我知道我可以在team模型中定义类似的东西，但它很详细并违反了demeter法则：

#models/team.rb
def contacts
  contacts_ary = []
  locations.each do |location|
    # team should not know the implementation of how location goes about grabbing contacts, thus breaking the law of demeter on the following line:
    location.contacts.each {|contact| contacts_ary << contact}
  end
  return contacts_ary
end

如何在遵守demeter定律的同时获取超出has_many :through关联的关联？

Answer 1

由于团队has_many :locations和地点has_many :contacts，我相信您只需将以下行添加到您的团队模型中：

has_many :contacts, through: :locations

然后，只需说出team.contacts即可检索团队的联系人。当然，为了实现这一目标，将在幕后加入很多SQL，但鉴于您的数据模型，这在任何情况下都是不可避免的。

在坚持德米特定律的同时抓住遥远的联想

1 个答案: