Re: searching for yoda - a developer's tale

dexter_at_uwm.edu
Date: 02/24/05 

Date: 24 Feb 2005 07:25:40 -0800

The mundane problems are with simply writing out the SQL queries to
include the JOIN clause(s) and not have any typos. Typos show up at
runtime and the error reported only gives you the line of the JDBC
call, not the particular SQL bit in question. This is tedious and
annoying, but by itself probably wouldn't force me to seek learning. A
similar problem is that with "standard" SQL there isn't an
INSERT_OR_UPDATE, and the format for said commands differs so one must
do a SELECT followed by an if (exists) UPDATE else INSERT. Effectively
writing three statements to perform one task. If there are many items
in your object graph that could be inserted/updated, the tedium (and
typos) increases.

The real problem though is worrying about persistence of object graphs.
 If I have a persistent object that has a collection of objects, then
the UPDATE statement (or really, the INSERT_OR_UPDATE bit) for the main
object needs to check each of the items in the collection to see if
they've changed (do an UPDATE), been deleted (do a DELETE), or been
added (do an INSERT). Suppose the relationship is bidirectional.
Suppose the collection is ordered (a List). One needs to pay close
attention to what the book "Hibernate In Action" terms "the scope of
object identity" -- what does it mean to say "this object has already
been saved, but has changed"? It implies you need your code to
maintain database keys which it shouldn't have to do.

All of these things end up making me have to think too hard about stuff
that the folks in relational db land have understood for decades. I
*believe* that Hibernate in particular has been able to shield the
developer from much of this. We work with objects. The
object/relational mapping problem is non-trivial and has been thought
about and implemented by folk with more time (and likely bigger brains)
than me -- and they've put their stuff out there for any to use....just
wish I knew how to take full advantage of it.

-don.

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