Question

I’m trying to set up a self-referential relationship, as described in this great video – http://railscasts.com/episodes/163-self-referential-association – and it’s mostly working, but not entirely working.

I have these entities: Users, who can either be a mentor or a mentee; Matches, which have a mentor_id (user.id), mentee_id (user.id), and status_id; and Statuses, which are a plain lookup table.

My User model looks like this:

class User < ActiveRecord::Base   

has_many :matches
has_many :mentors, :through => :matches
has_many :mentees, :through => :matches
has_many :statuses, :through => :matches

end

My Status model looks like this:

class Status < ActiveRecord::Base
  has_many :matches
end

My Match model looks like this:

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

When I puts user.mentors I get SQLite3::SQLException: no such column: matches.user_id: SELECT “users”.* FROM “users” INNER JOIN “matches” ON “users”.id = “matches”.mentor_id WHERE ((“matches”.user_id = 1))

Simply, I was hoping to do user.matches.find(1).status.id .. Any ideas on what I’m doing wrong?

Thanks in advance.
Jon

Answer 1

I’m pretty sure you’re looking for:

class User < ActiveRecord::Base
  has_many :match_mentors, :foreign_key => "mentee_id", :class_name => "Match"
  has_many :match_mentees, :foreign_key => "mentor_id", :class_name => "Match"

  has_many :mentors, :through => :match_mentors
  has_many :mentees, :through => :match_mentees

  def status_with_mentee mentee_id
    match = match_mentees.find_by_mentee_id(mentee_id)
    return nil if match.nil? 
    match.status
  end
end


class Match < ActiveRecord::Base
  belongs_to :mentor, :class_name => "User"
  belongs_to :mentee, :class_name => "User"
  belongs_to :status

  after_create :set_status

  def set_status
   Status.find(1).matches << self #replace 1 with the id you want
  end
end

Which gives:

u = User.create
u.mentors               => [] 
u.mentors.create        => #<User id: 2, name: nil, created_at: "2011-06-17 19:02:17", updated_at: "2011-06-17 19:02:17"> 
u.mentors               => [#<User id: 2, name: nil, created_at: "2011-06-17 19:02:17", updated_at: "2011-06-17 19:02:17">] 
v = u.mentors.first     => #<User id: 2, name: nil, created_at: "2011-06-17 19:02:17", updated_at: "2011-06-17 19:02:17"> 
v.mentees               => [#<User id: 1, name: nil, created_at: "2011-06-17 18:58:44", updated_at: "2011-06-17 18:58:44">] 

EDIT, to associate a mentee:

current_user.mentees << User.find(params[:mentee_id])

Rails will handle everything properly.

To know which is the relation between a mentor and one of his mentees:

current_user.status_with_mentee(params[:mentee_id])

Of course, you can create the same for mentor relationship