Help with completing-read

[Perry Smith]

The software I'm working on is doing this:

(let ((completing-read-func (if (null ido-mode)
                                  'completing-read
                                'ido-completing-read)))
    (setq ri-topic (or ri-topic
                       (funcall completing-read-func
                                "yari: "
                                (yari-ruby-obarray rehash)
                                nil
                                t
                                (yari-symbol-at-point)))))

The obarray has a list of methods with their complete class path like 
ActiveRecord::ConnectionAdapters::SchemaStatements#create_table

What I'd like to be able to do is allow the user to just type create_table and 
then
have a list of completions which would be the full class paths of for those
classes that have a create_table method.

What is the least painful way to do this?  I'm sorta ok competent with emacs 
lisp
but its not my strongest suit.

Thank you for your time,
Perry