Rails - Feb 2008 - Need help with self-referencing models and relationships

Okay,

I have the site running (http://www.londonprogressivejournal.com) and if
you look you can ''respond'' to any given article which leads to
you
submitting a ''letter'' object to the system.

At a later date we''ll be publishing these.

Articles can of course have many letters. Letters only have one article.

However, people will be able to respond to a published letter just as
they will to an article.

So a Letter can have many letters (those that are responses to it)...but
it also only has one letter if it is itself a response to an existing
letter.

My Letter model has both an article_id and a letter_id but my issue is
how to show Ruby that model? I have said ''has many letters''
but now of
course I can''t refer to letter.letter.id to find out which letter this
one might be a response to.

Does anyone know how to deal with this sort of self-referential
architecture in ruby?

Cheers
Theo
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You can define these relationships yourself using something like this:
class Letter < ActiveRecord::Base
  belongs_to :article
  belongs_to :parent, :foreign_key => ''parent_id'',
:class_name =>
''Letter''
  has_many :children, :foreign_key => ''parent_id, :class_name =>
''Letter'', :dependent => :destroy
end

But I would recommend taking a look at the acts_as_tree and
acts_as_nested_set plugins and see if they might provide what you are
looking for.  acts_as_tree provides the parent and children
associations like I listed above.  acts_as_nested set allows you to
retrieve all children in a single query.  (http://dev.rubyonrails.com/
svn/rails/plugins/)

Aaron

On Feb 4, 12:15 pm, Theo Graham-brown <rails-mailing-l...@andreas-
s.net> wrote:
> Okay,
>
> I have the site running (http://www.londonprogressivejournal.com) and if
> you look you can ''respond'' to any given article which
leads to you
> submitting a ''letter'' object to the system.
>
> At a later date we''ll be publishing these.
>
> Articles can of course have many letters. Letters only have one article.
>
> However, people will be able to respond to a published letter just as
> they will to an article.
>
> So a Letter can have many letters (those that are responses to it)...but
> it also only has one letter if it is itself a response to an existing
> letter.
>
> My Letter model has both an article_id and a letter_id but my issue is
> how to show Ruby that model? I have said ''has many
letters'' but now of
> course I can''t refer to letter.letter.id to find out which letter
this
> one might be a response to.
>
> Does anyone know how to deal with this sort of self-referential
> architecture in ruby?
>
> Cheers
> Theo
> --
> Posted viahttp://www.ruby-forum.com/.
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Theo Graham-brown wrote:
> Okay,
> 
> I have the site running (http://www.londonprogressivejournal.com) and if
> you look you can ''respond'' to any given article which
leads to you
> submitting a ''letter'' object to the system.
> 
> At a later date we''ll be publishing these.
> 
> Articles can of course have many letters. Letters only have one article.
> 
> However, people will be able to respond to a published letter just as
> they will to an article.
> 
> So a Letter can have many letters (those that are responses to it)...but
> it also only has one letter if it is itself a response to an existing
> letter.
> 
> My Letter model has both an article_id and a letter_id but my issue is
> how to show Ruby that model? I have said ''has many
letters'' but now of
> course I can''t refer to letter.letter.id to find out which letter
this
> one might be a response to.
> 
> Does anyone know how to deal with this sort of self-referential
> architecture in ruby?
> 
> Cheers
> Theo
Let me restate your problem from the Letter''s point of view.  A Letter 
belongs_to a parent (either a Article or another Letter).  It also 
has_many responses (always other letters).  I would build you letter 
class like this.

class Letter < ActiveRecord::Base
  belongs_to :parent, :polymorphic=>true
  has_many :responses, :class_name =>''Letter'',
:as=>:parent
end

Same thing for Article

class Article < ActiveRecord::Base
  has_many :letters, :as=>:parent
end

As a side benefit, you can attach a letter to anything else on your 
site.  You may also want to add validation on the belongs_to association 
to ensure that it only contains the classes you wish to attach letters 
to.

-- 
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