From: listrecv@...
Date: 2005-12-13T06:57:38+09:00
Subject: Re: Hibernate on Ruby

ActiveRecord is great for small-to-medium things, but does quickly show
it's limits on large things.  NOTE: Please, do not turn this thread
into a flame war.  See Martin Fowler's discussion of ActiveRecord
versus DataMapper.  Rails's ActiveRecord is based on Fowler's
ActiveRecord pattern, wheras Hibernate is a DataMapper, which Fowler
himself favors for complicated mappings.

See DHH's post:
"No, you don't get the full offer of opportunities that straight OO
with a data mapper holds. I'd like to think, though, that Active Record
gives you 80% of the features for 20% of the effort."
http://www.loudthinking.com/arc/000209.html

Example for me:
Let's say I have a class hierarchy, in which a particular field is
stored direclty in the db for one class, and calculated using a simple
SQL formula for other other classes.  How can I use the DB to query the
tree for all objects where field == aVal.

Answer: In ActiveRecord - you can't (w/o major hacking).  You need to
instantiate each one from the db, and then use Ruby to check each one.