与同一模型的多个关联

Question

我有两个类,我想指定如下:

class Club < ActiveRecord::Base
  belongs_to :president, :class_name => "Person", :foreign_key => "president_id"
  belongs_to :vice_president, 
             :class_name => "Person",
             :foreign_key => "vice_president_id"
end

class Person < ActiveRecord::Base
  has_one :club, :conditions => 
  ['president_id = ? OR vice_president_id = ?', '#{self.id}', '#{self.id}']
end

这不起作用,并在尝试从人物对象获得俱乐部关联时给出错误.错误是因为我在查看SQL时在俱乐部表中查找person_id.我可以通过声明多个has_one关联来解决它,但感觉这是不正确的做法.

一个人只能是一个俱乐部的总裁或副总裁.

任何能够就此问题提供一些建议的人,我都会非常感激.

Answer 1

has_one据我所知,你的病情永远不会在Rails中起作用.

在两个表上,每个"链接" 需要一个显式has_one或belongs_tohas_many.所以如果你有两个"链接",你需要两个has_one和两个belongs_to.这就是它的工作原理.

其次,我认为你应该重新考虑你的模型.你这样做的方式,一个人不能同时成为俱乐部和员工的总裁.或者是两个俱乐部的总裁.即使你现在没有这些,它们也可以在未来出现 - 现在更容易保持灵活性.

一种灵活的方法是使用has_many :through带有指定角色的中间表.换一种说法:

# The memberships table has a person_id, club_id and role_id, all integers

class Membership < ActiveRecord::Base
  belongs_to :club
  belongs_to :person
  validates_presence_of :role_id
  validates_numericality_of :role_id
end

class Club < ActiveRecord::Base
  has_many :memberships, :dependent => :delete_all
  has_many :people, :through => :memberships
end

class Person < ActiveRecord::Base
  has_many :memberships, :dependent => :delete_all
  has_many :clubs, :through => :memberships
end

现在,假设role_id = 0表示员工,role_id = 1表示总统,而role_id = 2表示vice_president,您可以像这样使用它:

tyler = Person.find(1) # person_id is 1
other = Person.find(2) # person_id is 2
c = Club.find(1)  # club_id is 1

tyler.clubs # returns all the clubs this person is "member" of
c.people # returns all the "members" of this club, no matter their role

#make tyler the president of c
tyler.memberships.create(:club_id => 1, :role_id => 1)

#make other the vicepresident of c
#but using c.memberships instead of other.memberships (works both ways)
c.memberships.create(:person_id => 2, :role_id => 1)

#find the (first) president of c
c.memberships.find_by_role_id(1).person

#find the (first) vicepresident of c
c.memberships.find_by_role_id(2).person

#find all the employees of c
c.memberships.find_all_by_role_id(0).collect { |m| m.person }

#find all the clubs of which tyler is president
tyler.memberships.find_all_by_role_id(1).collect { |m| m.club }

补充说明:

• 您可以使用角色表和模型来补充它.角色只有一个名字,角色会have_many关系和会员belong_to角色.或者,您可以在成员资格中定义获取角色名称的方法(如果为0,则返回"employee",如果为1,"President"等
• 您可以在成员身上添加验证,因此不能超过1人成为特定俱乐部的主席,或同一俱乐部的同一员工两次.稍后,如果你开始得到一个人需要在两个地方的"例外情况",你只需要调整你的验证.