Rails Model has_many with multiple foreign_keys

Question

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 b

Answer 1

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

def children
   children_of_mother.merge(children_of_father)
end

see this answer for more details

Answer 2

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

Answer 3

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 gender column and go with

  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 4

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)

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 5

Used named_scopes over the Person model do this:

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 6

I believe you can achieve the relationships you want using :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

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