From: Tobin Harris <comedyharris@...>
Date: 2002-05-20T03:29:10+09:00
Subject: Re: Object <-> Relational mapping

Hi there Thomas,

I posted a very similar question on comp.object (Relational Database
Persistance, 12th May 2002) , which is just fading out after load or
responses. Although people tend to go off on tangents somewhat, I did glean
the following:

Object Relational Mapping can be quite easy if you're not working against a
legacy database. Basically, the database becomes an 'skip' in which class
state (attributes) are stored. You can use reflection to automatically
generate the database schema from the object model, and I was told that this
can end up being quite normalised and freindly. Further maintenance from
there involves tweaking the mapping files, but not too much major work
apparently.

Things get trickier where you can't use this approach. You have to do much
more work - and I get the feeling this is the situation you're in. My
perspective was this, which some people agreed was about right!

"So you say you can do this with very little application code? How is this
so? I have build a object mappers in Visual Basic (which is unfortunately
what I'm working in at the mo). This worked will, but hardly required 'next
to no code'. For example, I had to explicitly code what fields mapped to
what columns for each object, where loading and saving. Also, I needed
caching to prevent bi-directional relationships from causing objects to keep
loading themselves. Finally, I had to put up with the trade-off of breaking
encapulation so that the mapping layer could access the data that neede
persisting in the objects. In the end, I'd say that I had almost as much
mapping code as the objects themselves!"

Since this topic is something that I'm still not settled with, I'd be
interested to hear how you get on. I'm facing the same difficulties, so if I
have any revelations I can share them with you.

HTH

Tobin Harris