Using a join model to relate a model to itself

Question

I have two models:

• User
• MentoringRelationship

MentoringRelationship is a join model that has a mentor_id column and a mentee_id column (both of these reference user_ids from the users table).

How can I specify a relation called 'mentees' on the User class that will return all of the users mentored by this user, using the MentoringRelationships join table? What relations do we need to declare in the User model and in the MentoringRelationship model?

Answer 1

You can do it using following ways. In user.rb

def mentees
 user = User.find_by_sql("select u.* from the users u, mentoring_relationships m where m.mentor_id = #{self.id} and u.id = m.mentee_id")
end

In controller

@user.mentees >> all of the users mentored by @user

Answer 2

Off the top of my head, referring to the API docs:

class User < AR::B
  has_many :mentees, :through => :mentoring_relationship
  has_many :mentors, :through => :mentoring_relationship
end

class MentoringRelationship < AR::B
  belongs_to :mentee, :class_name => "User"
  belongs_to :mentor, :class_name => "User"
end

Untested, but it seems like this should work.

Answer 3

I believe this works...

class User < ActiveRecord::Base
   has_many :mentees, :foreign_key => :mentee_id, 
      :class_name => "MentoringRelationship"

   has_many :mentors, :foreign_key => :mentor_id,
      :class_name => "MentoringRelationship"
end

class MentoringRelationship < ActiveRecord::Base
   belongs_to :mentee, :class_name => "User"
   belongs_to :mentor, :class_name => "User"   
end

With this code you can use

@user = User.find(:first)
@user.mentees
@user.mentors

Answer 4

Thanks to http://blog.hasmanythrough.com/2007/10/30/self-referential-has-many-through, I was able to put something together that works.

in app/models/user.rb

  has_many :mentee_relationships, :class_name => 'MentoringRelationship', :foreign_key => :mentor_id
  has_many :mentees, :through => :mentee_relationships, :source => :mentee, :foreign_key => :mentor_id

  has_many :mentor_relationships, :class_name => 'MentoringRelationship', :foreign_key => :mentee_id
  has_one :mentor, :through => :mentor_relationships, :source => :mentor, :foreign_key => :mentee_id

in app/models/mentoring_relationship.rb

  belongs_to :mentee, :class_name => "User"
  belongs_to :mentor, :class_name => "User"