# Deep nested associations on the same Model **URL:** \ **Category:** Rails\ **Created:** [September 1, 2009, 5:42pm UTC](https://www.ruby-forum.com/t/deep-nested-associations-on-the-same-model/174753 "2009-09-01T17:42:08Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![jbhruby](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/439d5e/32.png) [@jbhruby](https://www.ruby-forum.com/u/jbhruby)\ **Post date:** [September 1, 2009, 5:42pm UTC](https://www.ruby-forum.com/t/deep-nested-associations-on-the-same-model/174753/1 "2009-09-01T17:42:08Z")
This could be a lot simpler than I think and I’m just missing something obvious! I’m working on a creative collaboration app whereby one user could submit a Story and this can then be forked by another user and worked on seperately. To acheive this I have a has\_many association within the same Story model as such: class Story \< ActiveRecord::Base has\_many :forked\_stories, :class\_name =\> ‘Story’, :foreign\_key =\> :parent\_story\_id belongs\_to :parent\_story end In this way if a single story is an original it’s parent\_story\_id will be nil. Similarly, if I call @story.forked\_stories I can get a collection of all the stories that have been forked from the current one, or @story.parent\_story will return the story from which it has been forked. What I want is to be able to return all the forked\_stories and their forked\_stories for a given Story and I’m finding this very difficult since they’re all based on the same model. I keep running into dead ends. If I can return them to a certain depth as well that’d be great, so I’ve been trying to write a method that accepts a depth parameter but the crazy loops are frying my brain. Perhaps there’s something I can do with routes that would solve the problem? ---
**Author:** ![jbhruby](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/439d5e/32.png) [@jbhruby](https://www.ruby-forum.com/u/jbhruby)\ **Post date:** [September 1, 2009, 6:54pm UTC](https://www.ruby-forum.com/t/deep-nested-associations-on-the-same-model/174753/2 "2009-09-01T18:54:35Z")
Jon H. wrote: > This could be a lot simpler than I think and I’m just missing something > obvious! > > I’m working on a creative collaboration app whereby one user could > submit a Story and this can then be forked by another user and worked on > seperately. To acheive this I have a has\_many association within the > same Story model as such: > > class Story \< ActiveRecord::Base > > has\_many :forked\_stories, :class\_name =\> ‘Story’, :foreign\_key =\> > :parent\_story\_id > > belongs\_to :parent\_story > > end > > In this way if a single story is an original it’s parent\_story\_id will > be nil. Similarly, if I call @story.forked\_stories I can get a > collection of all the stories that have been forked from the current > one, or @story.parent\_story will return the story from which it has been > forked. So you have a tree structure of arbitrary depth? > What I want is to be able to return all the forked\_stories and their > forked\_stories for a given Story and I’m finding this very difficult > since they’re all based on the same model. I keep running into dead > ends. If I can return them to a certain depth as well that’d be great, > so I’ve been trying to write a method that accepts a depth parameter but > the crazy loops are frying my brain. There is a less obvious but ultimately much simpler way to do this. Use a nested-set data structure, which will make what you’re talking about pretty easy. The awesome\_nested\_set plugin would be just what you need. > Perhaps there’s something I can do with routes that would solve the > problem? No. Your issues have to do with data structure, not routing. ## Best, Marnen Laibow-Koser [http://www.marnen.org](http://www.marnen.org) removed\_email\_address@domain.invalid ---
**Author:** ![jbhruby](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/439d5e/32.png) [@jbhruby](https://www.ruby-forum.com/u/jbhruby)\ **Post date:** [September 2, 2009, 12:04pm UTC](https://www.ruby-forum.com/t/deep-nested-associations-on-the-same-model/174753/3 "2009-09-02T12:04:38Z")
On Sep 1, 5:42 pm, Jon H. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > What I want is to be able to return all the forked\_stories and their > forked\_stories for a given Story and I’m finding this very difficult > since they’re all based on the same model. I keep running into dead > ends. If I can return them to a certain depth as well that’d be great, > so I’ve been trying to write a method that accepts a depth parameter but > the crazy loops are frying my brain. As far as I can tell you have an algorithmical difficulty, not one related to Rails. To get back all the forked stories for a given story the following code snippet would do the job: def fork\_tree forked = forked\_stories forked\_from\_children = forked.inject([]) do |fstories, fstory| fstories + fstory.fork\_tree end forked + forked\_from\_children end (you can see the whole thing here: [story.rb · GitHub](http://gist.github.com/179186)) Note1: This has been tested under Ruby, not Rails Note2: The method is badly named, since it just returns an array, not a tree-like structure of all the stories forked directly from the story or from its children, or grandchildren, etc. Hope this helps, Bálint ---
**Author:** ![jbhruby](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/439d5e/32.png) [@jbhruby](https://www.ruby-forum.com/u/jbhruby)\ **Post date:** [September 2, 2009, 12:12pm UTC](https://www.ruby-forum.com/t/deep-nested-associations-on-the-same-model/174753/4 "2009-09-02T12:12:16Z")
Balint E. wrote: > On Sep 1, 5:42�pm, Jon H. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > > What I want is to be able to return all the forked\_stories and their > > forked\_stories for a given Story and I’m finding this very difficult > > since they’re all based on the same model. I keep running into dead > > ends. If I can return them to a certain depth as well that’d be great, > > so I’ve been trying to write a method that accepts a depth parameter but > > the crazy loops are frying my brain. > > As far as I can tell you have an algorithmical difficulty, not one > related to Rails. To get back all the forked stories for a given story > the following code snippet would do the job: > > def fork\_tree > forked = forked\_stories > forked\_from\_children = forked.inject([]) do |fstories, fstory| > fstories + fstory.fork\_tree > end > forked + forked\_from\_children > end > > (you can see the whole thing here: [story.rb · GitHub](http://gist.github.com/179186)) > > Note1: This has been tested under Ruby, not Rails > Note2: The method is badly named, since it just returns an array, not > a tree-like structure of all the stories forked directly from the > story or from its children, or grandchildren, etc. > > Hope this helps, > B�lint Note 3: Unless the whole array has already been loaded into memory, that’s horribly inefficient. Nested sets are the way to go here. ## Best, Marnen Laibow-Koser [http://www.marnen.org](http://www.marnen.org) removed\_email\_address@domain.invalid ---
**Author:** ![jbhruby](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/439d5e/32.png) [@jbhruby](https://www.ruby-forum.com/u/jbhruby)\ **Post date:** [September 2, 2009, 9:58pm UTC](https://www.ruby-forum.com/t/deep-nested-associations-on-the-same-model/174753/5 "2009-09-02T21:58:19Z")
> Note 3: Unless the whole array has already been loaded into memory, > that’s horribly inefficient. Nested sets are the way to go here. > > ## Best, > > ## Marnen Laibow-Koserhttp://www.marnen.org removed\_email\_address@domain.invalid > > Posted viahttp://www.ruby-forum.com/. Seems interesting, could you sketch up how that would work? Balint ---
**Author:** ![jbhruby](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/439d5e/32.png) [@jbhruby](https://www.ruby-forum.com/u/jbhruby)\ **Post date:** [September 3, 2009, 12:38am UTC](https://www.ruby-forum.com/t/deep-nested-associations-on-the-same-model/174753/6 "2009-09-03T00:38:17Z")
Balint E. wrote: > > Note 3: Unless the whole array has already been loaded into memory, > > that’s horribly inefficient. �Nested sets are the way to go here. > > > > ## Best, > > > > ## Marnen Laibow-Koserhttp://www.marnen.org removed\_email\_address@domain.invalid > > > > Posted viahttp://www.ruby-forum.com/. > > Seems interesting, could you sketch up how that would work? There are plenty of good articles available on nested sets (notably those by Joe Celko and Vadim Tropashko). Check 'em out, and also look at the awesome\_nested\_set rdoc! > Balint ## Best, Marnen Laibow-Koser [http://www.marnen.org](http://www.marnen.org) removed\_email\_address@domain.invalid Best