Rails - Sep 2010 - has_many and bi-directional relationships

I''m working on an app with a friend type system.  I currently have
setup like this with 2 tables.

users table keeps track of users

user_relationships table keeps track of friendships.  Now, there
should be two rows for each relationship.  This is to keep track of
the directional nature of the relationship between users. Each time a
relationship is made, both rows should be inserted into the table.

user_1 user_2 data
user_2 user_1 data

So what I can''t decide is what is the best way to implement these in
my rails app to be able to create a view of all user_relationships
with a given userid.

I can define a Relationship class, and mark User with has_many.  But
that will only select the relationships based on one column right?  So
it would look in one column and find all rows from that column. so if
I call User.relationships I will only have half of the relationship
info right?

So what I think i''m looking for is a way to overload the
User.relationships so that I can return a list of Relationships that I
compiled by making two queries, one on each column?

I can think of some other options that might work in this instance
(since i know there is always two rows of data I can just query on 1
column, and then in the Relationship model handle the dual column
nature of info), but I think it would still be interesting to know how
to overload the function, or describe this behavior better in my
model.

I hope this makes sense

Thanks

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pipplo wrote:
> I''m working on an app with a friend type system.  I currently have
> setup like this with 2 tables.
> 
> users table keeps track of users
> 
> user_relationships table keeps track of friendships.  Now, there
> should be two rows for each relationship.  This is to keep track of
> the directional nature of the relationship between users. Each time a
> relationship is made, both rows should be inserted into the table.
> 
> user_1 user_2 data
> user_2 user_1 data
[...]

That''s not necessarily a great idea.  Please see 
http://www.ruby-forum.com/topic/213468 .

Best,
--
Marnen Laibow-Koser
http://www.marnen.org
marnen-sbuyVjPbboAdnm+yROfE0A@public.gmane.org
-- 
Posted via http://www.ruby-forum.com/.

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How about something like this:

class User < ActiveRecord::Base
   has_many :relations, :foreign_key => "from_user"
end

class Relation < ActiveRecord::Base
   belongs_to :from_user, :class_name => "User", :foreign_key =>
"from_user"
   belongs_to :to_user, :class_name => "User", :foreign_key =>
"to_user"
end


To print list of all friends of , say, first user ind DB, you can something
like this:

User.first.relations.all.each { |r| puts r.to_user.name }


Here is Migrations for two tables:

class CreateUsers < ActiveRecord::Migration
  def self.up
    create_table :users do |t|
      t.string :name
      t.timestamps
    end
  end

  def self.down
    drop_table :users
  end
end


class CreateRelations < ActiveRecord::Migration
  def self.up
    create_table :relations do |t|
      t.integer :from_user
      t.integer :to_user
      # other data specific to relation
      t.timestamps
    end
  end

  def self.down
    drop_table :relations
  end
end

*****
It may have some gotchas, but can be enhanced.



On Thu, Sep 16, 2010 at 11:17 PM, Marnen Laibow-Koser
<lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org>wrote:
> pipplo wrote:
> > I''m working on an app with a friend type system.  I currently
have
> > setup like this with 2 tables.
> >
> > users table keeps track of users
> >
> > user_relationships table keeps track of friendships.  Now, there
> > should be two rows for each relationship.  This is to keep track of
> > the directional nature of the relationship between users. Each time a
> > relationship is made, both rows should be inserted into the table.
> >
> > user_1 user_2 data
> > user_2 user_1 data
> [...]
>
> That''s not necessarily a great idea.  Please see
> http://www.ruby-forum.com/topic/213468 .
>
> Best,
> --
> Marnen Laibow-Koser
> http://www.marnen.org
> marnen-sbuyVjPbboAdnm+yROfE0A@public.gmane.org
> --
> Posted via http://www.ruby-forum.com/.
>
> --
> You received this message because you are subscribed to the Google Groups
> "Ruby on Rails: Talk" group.
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>
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> .
> For more options, visit this group at
> http://groups.google.com/group/rubyonrails-talk?hl=en.
>
>
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its done here


http://railscasts.com/episodes/163-self-referential-association

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