From: Rob Sanheim <rsanheim@...>
Date: 2007-01-18T04:41:06+09:00
Subject: Re: ActiveRecord find_by_*() - how does it work?

Hi,

On 1/17/07, Eduardo Scoz <escoz@msn.com> wrote:
> Hi guys!
>
> I've been trying to understand how the find_by_*() method on
> ActiveRecord works, but couldn't find anything that could help. I think
> that you guys can probably help me on that.
>
> On Active Record, you can make a call like
>     user.find_by_first_name_and_last_name("eduardo"...)
> and this will generate the sql to send to the database.
>
> But how does that method gets created? ActiveRecord doesn't know what I
> want to find until I actually make the call, and the number of different
> combinations of parameters would probably be infinite for it to be
> created during the object initialization, so (I imagine) the method must
> be created __AFTER__ it was called.
>
> So my question is, is it possible for an object to receive a call to a
> method that doesn't exist, not throw a NoMethodError, and respond to
> that call?
>
> I hope my question makes sense! :)

Its a very good question.  Here are some references to help:

http://blog.hasmanythrough.com/2006/08/13/how-dynamic-finders-work
http://errtheblog.com/post/20
http://weblog.jamisbuck.org/2006/11/20/under-the-hood-activerecord-base-find-part-2
http://weblog.jamisbuck.org/2006/12/1/under-the-hood-activerecord-base-find-part-3
and of course, _Ruby for Rails_.

- Rob