Rails Model has_many with multiple foreign_keys - ruby-on-rails

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 basically what I want to do, but obviously I can't repeat the :children in a has_many (the first gets overwritten).
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?
Thanks!

Answer 1

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 2

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 3

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 4

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 ; )

Answer 5

My answer to Associations and (multiple) foreign keys in rails (3.2) : how to describe them in the model, and write up migrations is just for you!
As for your code,here are my modifications
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?

Answer 6

I prefer to use scopes for this issue. Like this:
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:
Person.children_for father_id, mother_id

Answer 7

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 8

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