Rails - Apr 2005 - Can you see an error? How debug?

Hi,
It is strange because in the first time that I use this function all is 
ok and in the second some times this return the value twofold.

    def self.getDirPath(parent_id)
        if nil == parent_id or 1 == Integer(parent_id)
            return ''./public/medias/''
        else
            parent = Media.find_by_id(parent_id)
            dirpath = ''''
            while nil != parent
                dirpath = parent.file + ''/'' + dirpath
                parent = Media.find_by_id(parent.parent_id)
            end
            return ''./public/'' + dirpath
        end
    end

More one think.
How do you debug in rubyonrails??

Thank you.

-- 

Pedro C. Valentini
pedro-p14LI7ZcAE/pVLaUnt/cCQC/G2K4zDHf@public.gmane.org
+55 (21) 8708-8035