# Self-referential :has\_many :through relationship? **URL:** \ **Category:** Rails\ **Created:** [October 29, 2007, 3:47am UTC](https://www.ruby-forum.com/t/self-referential-has-many-through-relationship/118575 "2007-10-29T03:47:56Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![dkanders](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/7bcc69/32.png) [@dkanders](https://www.ruby-forum.com/u/dkanders)\ **Post date:** [October 29, 2007, 3:47am UTC](https://www.ruby-forum.com/t/self-referential-has-many-through-relationship/118575/1 "2007-10-29T03:47:56Z")
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 ---
**Author:** ![dkanders](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/7bcc69/32.png) [@dkanders](https://www.ruby-forum.com/u/dkanders)\ **Post date:** [October 30, 2007, 8:18pm UTC](https://www.ruby-forum.com/t/self-referential-has-many-through-relationship/118575/2 "2007-10-30T20:18:13Z")
Dustin A. 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](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 S. [http://blog.hasmanythrough.com](http://blog.hasmanythrough.com) ---
**Author:** ![dkanders](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/7bcc69/32.png) [@dkanders](https://www.ruby-forum.com/u/dkanders)\ **Post date:** [October 29, 2007, 4:23am UTC](https://www.ruby-forum.com/t/self-referential-has-many-through-relationship/118575/3 "2007-10-29T04:23:49Z")
On 10/28/07, Dustin A. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > 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/](http://talklikeaduck.denhaven2.com/) ---
**Author:** ![dkanders](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/7bcc69/32.png) [@dkanders](https://www.ruby-forum.com/u/dkanders)\ **Post date:** [October 30, 2007, 9:57pm UTC](https://www.ruby-forum.com/t/self-referential-has-many-through-relationship/118575/4 "2007-10-30T21:57:18Z")
> Did you get this to work yet? I just posted an updated example of a > self-referential has\_many :through on my blog: > [has\_many :through - Self-referential has\_many :through associations](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 S. > [http://blog.hasmanythrough.com](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.