Rails - Oct 2007 - self-referential :has_many :through relationship?

Hi All,

I''m building an app that needs to make a comparison between two people
and I''m wondering how to best build the models, and if I''m
doing this
correctly.

I''m representing each partner as a User, so I wanted to keep just a
user
table and a comparisons table (the comparisons table will keep all the
comparison data, the user model will hold all the data about that
individual user)

I''m thinking of making a User-to-User self-referential join through a
"comparison" model.

So, I''d have two models:  the user model, and a comparison model

The user model would look something like this:
class User < ActiveRecord::Base
  belongs_to :partner, :through => :comparisons
end

and the comparisons:

class Comparison < ActiveRecord::Base
  belongs_to :user
  has_one :partner, :class_name => "User", :foreign_key =>
"partner_id"
end

I honestly have no idea if this will work... does this look close?

Thanks in advance!
Dustin
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On 10/28/07, Dustin Anderson
<rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:
>
> Hi All,
>
> I''m building an app that needs to make a comparison between two
people
> and I''m wondering how to best build the models, and if
I''m doing this
> correctly.
>
> I''m representing each partner as a User, so I wanted to keep just
a user
> table and a comparisons table (the comparisons table will keep all the
> comparison data, the user model will hold all the data about that
> individual user)
>
> I''m thinking of making a User-to-User self-referential join
through a
> "comparison" model.
>
> So, I''d have two models:  the user model, and a comparison model
>
> The user model would look something like this:
> class User < ActiveRecord::Base
>   belongs_to :partner, :through => :comparisons
:through is not a valid option on belongs_to, you can only use it on :has_many

.....
>
> I honestly have no idea if this will work... does this look close?
Sorry, don''t think so.

Maybe with a little more insight on what you''re trying to do with the
comparison Model, someone can move you towards the goal.
-- 
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denhaven2.com/

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Dustin Anderson wrote:
> I''m building an app that needs to make a comparison between two
people
> and I''m wondering how to best build the models, and if
I''m doing this
> correctly.
> 
> I''m representing each partner as a User, so I wanted to keep just
a user
> table and a comparisons table (the comparisons table will keep all the
> comparison data, the user model will hold all the data about that
> individual user)
> 
> I''m thinking of making a User-to-User self-referential join
through a
> "comparison" model.
> 
> So, I''d have two models:  the user model, and a comparison model
> 
> The user model would look something like this:
> class User < ActiveRecord::Base
>   belongs_to :partner, :through => :comparisons
> end
> 
> and the comparisons:
> 
> class Comparison < ActiveRecord::Base
>   belongs_to :user
>   has_one :partner, :class_name => "User", :foreign_key =>
"partner_id"
> end
> 
> I honestly have no idea if this will work... does this look close?
Did you get this to work yet? I just posted an updated example of a 
self-referential has_many :through on my blog:
http://blog.hasmanythrough.com/2007/10/30/self-referential-has-many-through
You might find that helpful.

If you really need an asymmetric join model, I''m interested in seeing 
what you put together. I was thinking about blogging an example of that 
too, but I couldn''t think up a good use for it.

--
Josh Susser
http://blog.hasmanythrough.com
-- 
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> Did you get this to work yet? I just posted an updated example of a 
> self-referential has_many :through on my blog:
> http://blog.hasmanythrough.com/2007/10/30/self-referential-has-many-through
> You might find that helpful.
> 
> If you really need an asymmetric join model, I''m interested in
seeing
> what you put together. I was thinking about blogging an example of that 
> too, but I couldn''t think up a good use for it.
> 
> --
> Josh Susser
> http://blog.hasmanythrough.com
Well, what I''m trying to do is compare two people - through a photo... 
I''m using attachment_fu.  Here''s what I have at this point...
I actually
did away with the User model all together and just made the comparisons 
hold all the foreign keys:

Comparisons model:
  belongs_to  :male_partner, :polymorphic => true
  belongs_to  :female_partner, :polymorphic => true

(Fields for comparisons):
    t.column "male_partner_id",    :integer
    t.column "male_partner_type",  :string
    t.column "female_partner_id",   :integer
    t.column "female_partner_type", :string
    t.column "comparison_value",  :float

MalePartner
  has_many :comparisons, :as => :male_partner

FemalePartner
  has_many :comparisons, :as => :female_partner

That''s it, again, no idea if it will work...  The reason I made the 
male_partner and female_partner polymorphic is to be able to use an 
image from the web instead of an uploaded image.  This is for a dating 
site.

Thanks for the blog Josh, I checked it out... very cool - a little more 
that I need for this (I think), but nonetheless, it''s cool to see that 
all those self-referential joins can be done.

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