Question

相对较新的rails并尝试使用具有name，gender，father_id和mother_id（2个父项）的单个Person模型来建模一个非常简单的族“树”。下面基本上是我想要做的，但显然我不能重复：has_many中的孩子（第一个被覆盖）。

class Person < ActiveRecord::Base
  belongs_to :father, :class_name => 'Person'
  belongs_to :mother, :class_name => 'Person'
  has_many :children, :class_name => 'Person', :foreign_key => 'mother_id'
  has_many :children, :class_name => 'Person', :foreign_key => 'father_id'
end

是否有一种简单的方法可以将has_many与2个外键一起使用，或者根据对象的性别更改外键？或者还有其他/更好的方式吗？

谢谢！

Answer 1

在IRC上找到一个似乎有用的简单答案（感谢雷达）：

class Person < ActiveRecord::Base
  belongs_to :father, :class_name => 'Person'
  belongs_to :mother, :class_name => 'Person'
  has_many :children_of_father, :class_name => 'Person', :foreign_key => 'father_id'
  has_many :children_of_mother, :class_name => 'Person', :foreign_key => 'mother_id'
  def children
     children_of_mother + children_of_father
  end
end

Answer 2

要改进Kenzie的答案，您可以通过定义Person#children来实现ActiveRecord关系：

def children
   children_of_mother.merge(children_of_father)
end

有关详细信息，请参阅this answer

Answer 3

在Person模型上使用named_scopes 这样做：

class Person < ActiveRecord::Base

    def children
      Person.with_parent(id)
    end

    named_scope :with_parent, lambda{ |pid| 

       { :conditions=>["father_id = ? or mother_id=?", pid, pid]}
    }
 end

Answer 4

我相信你可以使用：has_one。

来实现你想要的关系

class Person < ActiveRecord::Base
  has_one :father, :class_name => 'Person', :foreign_key => 'father_id'
  has_one :mother, :class_name => 'Person', :foreign_key => 'mother_id'
  has_many :children, :class_name => 'Person'
end

下班后我会确认并编辑这个答案; ）

Answer 5

我更喜欢使用范围来解决这个问题。像这样：

class Person < ActiveRecord::Base
  belongs_to :father, :class_name => 'Person'
  belongs_to :mother, :class_name => 'Person'
  has_many :children_of_father, :class_name => 'Person', :foreign_key => 'father_id'
  has_many :children_of_mother, :class_name => 'Person', :foreign_key => 'mother_id'

  scope :children_for, lambda {|father_id, mother_id| where('father_id = ? AND mother_id = ?', father_id, mother_id) }
end

这个技巧可以让没有使用实例的孩子轻松获得：

Person.children_for father_id, mother_id

Answer 6

不是所述一般问题的解决方案（＆＃34; has_many有多个外键＆＃34;），但是，如果某人可以是母亲或父亲，但不是两者，我会添加{ {1}}列，然后选择

gender

Answer 7

我对Associations and (multiple) foreign keys in rails (3.2) : how to describe them in the model, and write up migrations的回答仅适合您！

至于你的代码，这是我的修改

class Person < ActiveRecord::Base
  belongs_to :father, :class_name => 'Person'
  belongs_to :mother, :class_name => 'Person'
  has_many :children, ->(person) { unscope(where: :person_id).where("father_id = ? OR mother_id = ?", person.id, person.id) }, class_name: 'Person'
end

那么有问题吗？

Answer 8

我一直在寻找相同的功能，如果您不希望返回一个数组而不是ActiveRecord::AssociationRelation，则可以使用<<代替+。（See the ActiveRecord documentation）

class Person < ActiveRecord::Base
  belongs_to :father, :class_name => 'Person'
  belongs_to :mother, :class_name => 'Person'

  has_many :children_of_father, :class_name => 'Person', :foreign_key => 'father_id'
  has_many :children_of_mother, :class_name => 'Person', :foreign_key => 'mother_id'

  def children
     children_of_mother << children_of_father
  end
end

Rails模型has_many有多个foreign_keys

8 个答案: