Rails - Apr 2006 - table that have many-to-may relationship to itself

In a social netowrk data model, users belongs other users, and can have 
many friends as users, so it is a many to many relatioship.

the class definition could be

class User < ApplicationController
   has_mang_ang_belongs_to users


But how it looks like in the mysql database tables in a "joined" 
users
table.

The question really is: what is the table looks like when a model has 
many and belongs itself.

thx

-- 
Posted via http://www.ruby-forum.com/.

Hi,

This example is right out of the Rails Recipes book by Chad Fowler 
(http://www.pragmaticprogrammer.com/titles/fr_rr/index.html):

Assume that you have people and people have friends. Just as you''ve 
described, this is a habtm relationship that refers back to the same 
table. Whenever you have a habtm, you need a join table. Here''s a 
(partial) migration that describes the two tables:

create_table :people do |t|
  t.column "name", :string
end
create_table :friends_people, :id => false do |t|
  t.column "person_id", :integer
  t.column "friend_id", :integer
end

And now here is the ActiveRecord model:

class Person < ActiveRecord::Base
  has_and_belongs_to_many :friends,
    :class_name => "Person",
    :join_table => "friends_people",
    :association_foreign_key => "friend_id",
    :foreign_key => "person_id"
end

brian

-- 
Posted via http://www.ruby-forum.com/.

You''re talking about a self-referential many-many relationship. The 
Rails Recipes book has an example of how to do this, plus there are a 
few other things in various places. Try googling "ruby rails 
self-referential"

liang gao wrote:
> In a social netowrk data model, users belongs other users, and can have 
> many friends as users, so it is a many to many relatioship.
>
> the class definition could be
>
> class User < ApplicationController
>    has_mang_ang_belongs_to users
>
>
> But how it looks like in the mysql database tables in a "joined" 
users
> table.
>
> The question really is: what is the table looks like when a model has 
> many and belongs itself.
>
> thx
>
>