How to access attribute in a self-referential many-to-many r

Rails
1

Hello List,

I created a self-referential many-to-many relationship (as described
in the book Rails recipe #18), where I have a model that has
many-to-many relationships with itself. In this case, it’s person who
can become friends. The join table looks like this:

mysql> select * from friends_people;
±----------±----------±----------+
| person_id | friend_id | confirmed |
±----------±----------±----------+
| 1 | 2 | NULL |
| 2 | 1 | NULL |
| 1 | 3 | NULL |
| 3 | 1 | NULL |

and the people table is
mysql> select * from people;
±------------+
| id | name |
±—±-------+
| 1 | ren |
| 2 | amy |
±—±-------+

I have a model for person.rb, but none for friends_people. I can add
friends like this:
person1.friends << person2

Now the question is: how do I access the boolean “confirmed” from my
model person.rb? Is this possible, and what is the best way?

Thanks in advance,
Renaud

2

This is probably the best article to read about this:

http://blog.hasmanythrough.com/articles/2006/04/21/self-referential-through

In your case (and shamelessly ripping off Josh’s code replacing Edge
with Friendship and Node with User) it might be a bit like this:

create_table “users” do |t|
t.column “name”, :string
end
create_table “friendships” do |t|
t.column “source_id”, :integer, :null => false
t.column “sink_id”, :integer, :null => false
t.column “confirmed”, :boolean

class Friendship < ActiveRecord::Base
belongs_to :source, :foreign_key => “source_id”, :class_name => “User”
belongs_to :sink, :foreign_key => “sink_id”, :class_name => “User”
end

class User < ActiveRecord::Base
has_many :friendships_as_source, :foreign_key => ‘source_id’,
:class_name => ‘Friendship’
has_many :friendships_as_sink, :foreign_key => ‘sink_id’,
:class_name => ‘Friendship’
has_many :people_who_like_me, :through => :friendships_as_sink
has_many :people_i_like, :through => :friendships_as_source
end

now, depending on your specific needs, you can reference

user.friendships_as_source.select {|friendship| friendship.confirmed}

or similar.

Cameron

3

Thank you Cameron, this works well.

However, I’m not sure how to access the “friends”:

person1.find_all_in_people_i_like
/usr/lib/ruby/gems/1.8/gems/activerecord-1.14.3/lib/active_record/associations.rb:873:
warning: instance variable @people_i_like not initialized
ActiveRecord::HasManyThroughSourceAssociationNotFoundError:
ActiveRecord::HasManyThroughSourceAssociationNotFoundError

but this works:
person1.find_all_in_friendships_as_source

also, is there a easier way to create new friends than:
person1.friendships_as_source.create(:sink_id =>33, :confirmed => true)

Any hints?

Thanks,
Renaud

PS: the Rails community rocks, I am very impressed!