Rails模型has_many与多个foreign_keys

Question

相对较新的轨道，并试图用一个名称，性别，father_id和mother_id（父母）的单人模型来建模一个非常简单的家庭“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 

是否有与2个外键使用的has_many，或者可能改变基于对象的性别外键的简单方法？或者还有其他更好的方法吗？

谢谢！

Answer 1

发现IRC上一个简单的答案，似乎工作（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

我相信你可以实现你想使用的关系：has_one。

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 

我会在下班后确认并编辑此答案; ）

Answer 3

使用在Person模型named_scopes 做到这一点：

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

我更喜欢使用范围为这个问题。就像这样：

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 

这招可以很容易地让孩子们在不使用实例：

Person.children_for father_id, mother_id 

Answer 5

为了改善Kenzie的回答，您可以实现一个ActiveRecord关系定义Person#children，如：

def children 
    children_of_mother.merge(children_of_father) 
end 

看到this answer更多细节

Answer 6

不是解决所述的一般问题（“有多个外键的has_many”），但是，鉴于一个人既可以是母亲也可以是父亲，但不是两者，我将添加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 

Answer 7

我一直在寻找相同的功能，如果你不想返回一个数组而不是ActiveRecord::AssociationRelation，你可以使用<<而不是+。 （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 

Answer 8

我的回答Associations and (multiple) foreign keys in rails (3.2) : how to describe them in the model, and write up migrations是只为你！

至于你的代码，这里有我的修改

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 

所以什么问题吗？