Rails - Dec 2004 - How do I overwrite AR-created magic methods?

Hi,

how do I overwrite the size method that gets created by AR (or is it?). 
Example:

I have a model with

class Contentnode < ActiveRecord::Base
   has_many :children, :class_name => ''Contentnode'',
:finder_sql =>
     ''SELECT * FROM contentnodes
      WHERE id <> #{id} AND lft BETWEEN #{lft} AND #{rgt}''
...
end

Now when in my code I do a

node = Contentnode.find(1) # this is root
node.children.size #-> 9

It seems that the size method is created by AR. It emit the following SQL

SELECT * FROM contentnodes WHERE id = ''1''
SELECT COUNT(*) FROM contentnodes WHERE id <> 1 AND lft BETWEEN 1 AND 18

which is correct, but not what I want. I want to be able to overwrite 
the #size method so I can issue my own query or behaviour. How do I do that?

-- 
Sascha Ebach

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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

Best,
jeremy
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Hi Jeremy,

Jeremy Kemper wrote:
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> Hash: SHA1
> 
> 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