Ruby-on-rails 带有多个外键的 Rails 模型 has_many

Rails Model has_many with multiple foreign_keys

提问by Kenzie

Relatively new to rails and trying to model a very simple family "tree" with a single Person model that has a name, gender, father_id and mother_id (2 parents). Below is basically what I want to do, but obviously I can't repeat the :children in a has_many (the first gets overwritten).

Rails 相对较新，并尝试使用具有姓名、性别、father_id 和 Mother_id（2 个父母）的单个 Person 模型对非常简单的家庭“树”进行建模。下面基本上是我想要做的，但显然我不能重复 has_many 中的 :children （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

Is there a simple way to use has_many with 2 foreign keys, or maybe change the foreign key based on the object's gender? Or is there another/better way altogether?

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？或者有另一种/更好的方法吗？

Thanks!

谢谢！

采纳答案by Kenzie

Found a simple answer on IRC that seems to work (thanks to Radar):

在 IRC 上找到了一个似乎有效的简单答案（感谢 Radar）：

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

回答by stevenspiel

To improve on Kenzie's answer, you can achieve an ActiveRecord Relation by defining Person#childrenlike:

为了改进Kenzie的答案，您可以通过定义以下内容来实现 ActiveRecord Relation Person#children：

def children
   children_of_mother.merge(children_of_father)
end

see this answerfor more details

有关更多详细信息，请参阅此答案

回答by Zando

Used named_scopes over the Person model do this:

在 Person 模型上使用 named_scopes 执行以下操作：

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

回答by Gordon Wilson

I believe you can achieve the relationships you want using :has_one.

我相信您可以使用 :has_one 实现您想要的关系。

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

I'll confirm and edit this answer after work ; )

我会在下班后确认并编辑这个答案；)

回答by squiter

I prefer to use scopes for this issue. Like this:

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

This trick make it easy to get children without use instances:

这个技巧可以很容易地在没有使用实例的情况下获得孩子：

Person.children_for father_id, mother_id

回答by Tom Locke

Not a solution to the general question as stated ("has_many with multiple foreign keys"), but, given a person can either be a mother or a father, but not both, I would add a gendercolumn and go with

不是如上所述的一般问题的解决方案（“has_many 带有多个外键”），但是，鉴于一个人可以是母亲或父亲，但不能同时是两者，我会添加一gender列并使用

  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
    gender == "male" ? children_of_father : children_of_mother
  end

回答by Anthony Mangiavellano

I was looking for the same feature, if you don't want to return an array but a ActiveRecord::AssociationRelation, you can use <<instead of +. (See the ActiveRecord documentation)

我正在寻找相同的功能，如果您不想返回数组而是 a ActiveRecord::AssociationRelation，则可以使用<<代替+. （请参阅 ActiveRecord 文档）

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

回答by sunsoft

My answer to Associations and (multiple) foreign keys in rails (3.2) : how to describe them in the model, and write up migrationsis just for you!

我对Rails (3.2) 中的关联和（多个）外键的回答：如何在模型中描述它们，并编写迁移只适合您！

As for your code,here are my modifications

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

So any questions?

那么有什么问题吗？