使用多态多对多自引用关系以及 Rails 中关系上的属性

Question

我想在 Rails 中创建自引用关系。我有一个 Person 模型，该人应该有具有相同 Person 对象的大师和学生。

到目前为止，我尝试过：

class Person <ActiveRecord::Base
   has_many :relationships, :dependent => :destroy
   has_many :masters, :through => :relationships, :conditions => "status='master'"
   has_many :pupils, :through => :relationships, :conditions => "status='pupil'"
   has_many :inverse_relationships, :class_name => "Relationship",
      :foreign_key => "related_id"
   has_many :inverse_masters, :through => :inverse_relationships,  
      :source => :person, :conditions => "status='master'"
   has_many :inverse_pupils, :through => :inverse_relationships,  
      :source => :person, :conditions => "status='pupil'"
end

class Relationship < ActiveRecord::Base
  belongs_to :person
  belongs_to :master, :class_name => "Person", :foreign_key => 'related_id'
  belongs_to :pupil, :class_name => "Person", :foreign_key => 'related_id'
end

当我尝试选择时，它似乎有效：

@a = Person.find(:first)
@a.masters

但是当我尝试推送到主控时，它会保存关系，而不会将状态设置为主控。它会保存 null。有没有一种简单的方法可以在我推入大师时保存 status=master 并在推入学生时保存 status=pupil ？

谢谢

Answer 1

简而言之，解决方案是：关联回调（更多信息请参见关联回调部分：http://railsapi.com/doc/rails-v3.0.0/classes/ActiveRecord/Associations/ClassMethods.html）

为了更详细一点，我对您的示例进行了一些调整位，但基本上结构是相同的，这里是代码：

class Person < ActiveRecord::Base
  has_many :relationships
  has_many :pupils, :through => :relationships, :source => :other_person, :conditions => 'relationships.type = "MasterPupil"', :after_add => Proc.new{|p,o| Relationship.update_all("type = 'MasterPupil'", ['person_id = ? AND other_person_id = ?', p.id, o.id])}
  has_many :masters, :through => :relationships, :source => :other_person, :conditions => 'relationships.type = "PupilMaster"', :after_add => Proc.new{|p,o| Relationship.update_all("type = 'PupilMaster'", ['person_id = ? AND other_person_id = ?', p.id, o.id])}
end

class Relationship < ActiveRecord::Base
  belongs_to :person
  belongs_to :other_person, :class_name => 'Person'
  before_validation :set_type

  def set_type
    self.type = 'OpenRelationship'
  end
end

class MasterPupil < Relationship
end

class PupilMaster < Relationship
end

RelationShip 模型包含一个类型列，它相当于您的状态列，但如果我以后想做 STI 并声明 MasterPupil/PupilMaster 关系模型，类型会更好。

RelationShip 还有一个 set_type before_validation ，它将类型设置为 OpenRelationship ，这应该是临时的，然后在每个关联中的 Person 模型中定义的 after_add 回调将事情搞清楚（并设置 MasterPupil 或 PupilMaster 类型）

，现在：

Loading development environment (Rails 3.0.0)
irb(main):001:0> p = Person.create
=> #<Person id: 1, created_at: "2010-09-10 23:35:37", updated_at: "2010-09-10 23:35:37">
irb(main):002:0> p.pupils
=> []
irb(main):003:0> p.masters
=> []
irb(main):004:0> p.pupils << Person.create
=> [#<Person id: 2, created_at: "2010-09-10 23:35:56", updated_at: "2010-09-10 23:35:56">]
irb(main):005:0> Relationship.all
=> [#<MasterPupil id: 1, person_id: 1, other_person_id: 2, type: "MasterPupil">]
irb(main):006:0> p.masters << Person.create
=> [#<Person id: 3, created_at: "2010-09-10 23:36:29", updated_at: "2010-09-10 23:36:29">]
irb(main):007:0> Relationship.all
=> [#<MasterPupil id: 1, person_id: 1, other_person_id: 2, type: "MasterPupil">, #<PupilMaster id: 2, person_id: 1, other_person_id: 3, type: "PupilMaster">]
irb(main):008:0> p.reload
=> #<Person id: 1, created_at: "2010-09-10 23:35:37", updated_at: "2010-09-10 23:35:37">
irb(main):009:0> p.pupils
=> [#<Person id: 2, created_at: "2010-09-10 23:35:56", updated_at: "2010-09-10 23:35:56">]
irb(main):010:0> p.masters
=> [#<Person id: 3, created_at: "2010-09-10 23:36:29", updated_at: "2010-09-10 23:36:29">]