[Rails] How do I overwrite AR-created magic methods?

[Sascha Ebach]

Hi Jeremy,

Jeremy Kemper wrote:
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> Sascha Ebach wrote:
> | how do I overwrite the size method that gets created by AR (or is it?).
> 
> Here is a patch which adds :counter_sql option for has_many.
> ~  http://dev.rubyonrails.org/trac.cgi/ticket/265
> 
> ~  class Contentnode < ActiveRecord::Base
> ~    has_many :children, :class_name => 'Contentnode',
> ~             :finder_sql  => 'SELECT * FROM contentnodes ...'
> ~             :counter_sql => 'SELECT COUNT(*) FROM contentnodes ...'
> ~  end

Thank you for the patch. It will be useful for other cases. But, 
actually, in this case I don't want to issue another sql statement. I 
better explain a little more.

I use preorder tree traversal in my CMS. Very much like here:

http://rforum.andreas-s.net/trac/file/rforum/app/models/post.rb

The thing is. Since this mechanism provides a way to extract the size of 
a subtree without doing a query. You can read about that here:

http://www.sitepoint.com/print/hierarchical-data-database (under 
Headline "How Many Descendants")

children.size = (right – left - 1) / 2

So to get the number of children I can simply do a little math without 
the roundtrip to the database, which is what I was trying to avoid ;)

I would like to have something like this

def size
   # no sql query here since none is needed
   (self.rgt - self.lft - 1) / 2
end

-- 
Sascha Ebach