From: Hal Fulton <hal9000@...>
Date: 2006-01-09T12:34:46+09:00
Subject: Re: Ideas on "Why Living Dangerous can be A Good Thing" in Ruby?

Steve Litt wrote:
> 
> I'm trying to understand this. If Model.find_by_city was never defined, how 
> can it know what to do? I think I'm missing some big chunk of Ruby knowledge 
> here.
> 
> Are you saying that when Model.find_by_city is executed, the model looks at 
> the database, discovers there's a city column, and on the fly constructs a 
> method to search the table by city?
> 

What you're missing is method_missing.  :)

When a method doesn't exist, method_missing gets called. There's a default
one that raises an exception, but you can override it with any behavior
you want.

The name of the called method is passed in, e.g., "find_by_city"; so if you
parse it and see that it has the form "find_by_X" then you can know that X
is (supposed to be) a field name. Then you just handle it.

A variation on this is to define the method so that next time, method_missing
will not be called on that name.

Makes sense?


Hal