Parent-child relationship in User model (self join) - ruby-on-rails

Question

In rails, I have this User model:
class User < ActiveRecord::Base
enum role: [:adult, :child, :admin]
after_initialize :set_default_role, :if => :new_record?
# belongs_to :spouse, :foreign_key => :spouse_id, :class_name => 'User', :inverse_of => :spouse
def set_default_role
self.role ||= :adult
end
# Include default devise modules. Others available are:
# :confirmable, :lockable, :timeoutable and :omniauthable
devise :database_authenticatable, :registerable, :confirmable,
:recoverable, :rememberable, :trackable, :validatable
def marry(user)
self.spouse = user
user.spouse = self
end
end
I added spouses through this migration:
class AddFieldsToUser < ActiveRecord::Migration
def change
# for marriages
add_column :users, :spouse_id, :integer, index: true
end
end
and that works decently (though my inverse of function never worked # belongs_to :spouse, :foreign_key => :spouse_id, :class_name => 'User', :inverse_of => :spouse
). I am now trying to do another self join with a "child-parent" relationship. A parent can have many children and a child can have (many / two) parents. This is the migration I came up with:
class CreateParentalRelationships < ActiveRecord::Migration
def change
create_table :parental_relationships do |t|
t.references :parent, index: true
t.references :child
end
end
end
and I added this to the model:
has_many :children, :through => :parental_relationships, class_name: "User"
has_many :parents, :through => :parental_relationships, class_name: "User"
but the relationship did not work with the following error:
[7] pry(main)> u = User.find(3)
User Load (0.0ms) SELECT "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1 [["id", 3]]
=> #<User id: 3, email: ...>
[8] pry(main)> u.children
ActiveRecord::HasManyThroughAssociationNotFoundError: Could not find the association :parental_relationships in model Us
er
[9] pry(main)> u.parent
NoMethodError: undefined method `parent' for #<User:0x5e52eb0>
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/activemodel-4.1.8/lib/active_model/attribute_methods.rb:435:in
`method_missing'
[10] pry(main)> u.parents
ActiveRecord::HasManyThroughAssociationNotFoundError: Could not find the association :parental_relationships in model Us
er
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/reflection.rb:690:in `che
ck_validity!'
[11] pry(main)> u2.children
ActiveRecord::HasManyThroughAssociationNotFoundError: Could not find the association :parental_relationships in model Us
er
from C:/RailsInstaller/Ruby2.1.0/lib/ruby/gems/2.1.0/gems/activerecord-4.1.8/lib/active_record/reflection.rb:690:in `che
ck_validity!'
What am I missing?

Answer 1

Setting up the parent child relationship takes some finagling.
class ParentalRelationship < ActiveRecord::Base
belongs_to :parent, class_name: 'User'
belongs_to :child, class_name: 'User'
end
class User < ActiveRecord::Base
has_many :parent_relationships,
foreign_key: 'child_id',
class_name: 'ParentalRelationship'
has_many :child_relationships,
foreign_key: 'parent_id',
class_name: 'ParentalRelationship'
has_many :parents,
through: :parent_relationships,
class_name: 'User'
has_many :children,
through: :child_relationships,
class_name: 'User'
has_and_belongs_to_many :marriages
belongs_to :current_marriage, class_name: 'Marriage'
def marry(spouse)
marriage = Marriage.create(users: [self, spouse])
marriage.users.each { |u| u.update(current_marriage: marriage ) }
marriage
end
def spouse
return nil unless current_marriage
current_marriage
.users.where.not('marriages_users.user_id' => id).first
end
def birth(child)
child.parents << self
child.parents << spouse if spouse
end
end
Note that we need to setup the relation to ParentalRelationship twice since we need to tell rails which foreign key it should look at for each type of relation (user is parent or child).
Since in these modern times people can actually have be married several times we need a Marriage model and a join table for users_marriages.
class Marriage < ActiveRecord::Base
has_and_belongs_to_many :users
validates :users, length: { minimum: 2, maximum: 2 }
end
rails g migration CreateUsersMarriagesJoinTable users marriages
Example app with specs: https://github.com/maxcal/sandbox/tree/31614819

Answer 2

I came up with a solution. Not sure if it is the best:
my new User model:
class User < ActiveRecord::Base
enum role: [:adult, :child, :admin]
after_initialize :set_default_role, :if => :new_record?
belongs_to :spouse, :foreign_key => :spouse_id, :class_name => 'User', :inverse_of => :spouse
has_many :parental_relationships
has_many :children, :through => :parental_relationships, class_name: 'User'
has_many :parents, :through => :parental_relationships, class_name: 'User'
def set_default_role
self.role ||= :adult
end
# Include default devise modules. Others available are:
# :confirmable, :lockable, :timeoutable and :omniauthable
devise :database_authenticatable, :registerable, :confirmable,
:recoverable, :rememberable, :trackable, :validatable
def marry(user)
self.spouse = user
user.spouse = self
end
def birth(user)
self.children << user
user.parents << self
if self.spouse
self.spouse.children << user
user.parents << self.spouse
end
end
end
I had to edit a few migrations and models.
ParentalRelationships migration
class CreateParentalRelationships < ActiveRecord::Migration
def change
create_table :parental_relationships do |t|
t.references :user, index: true
t.references :child
t.references :parent
end
end
end
ParentalRelationship model:
class ParentalRelationship < ActiveRecord::Base
belongs_to :user
# , :class_name => "User"
# belongs_to :parent, :class_name => "User"
belongs_to :child, :class_name => "User"
belongs_to :parent, :class_name => "User"
end
So, to add relationships:
u = User.find(50)
u.birth(User.find(60))