From: Warren Young
Date: December 3 2008 11:39pm
Subject: Re: Using macros to compose SSQLS structures.
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Ryan W. Frenz wrote:
> 
> Is it blatantly wrong to think that I can guarantee
> that each object has a unique id?  Because I'm definitely assuming
> that (and enforcing it in client code) right now.  The system is
> self-contained (i.e. my app is the only entity accessing the
> database).

I'd assumed these id columns were AUTO_INCREMENT, in which case there is 
no way to ensure the values are unique across multiple tables without 
ugly hackery.

If your program generates the values, that works only so long as you 
only run a single instance of the program at a time.  Even running two 
copies on the same machine by accident can roach your DB.  Don't tell me 
you've never seen an impatient user double-click a slow-launching 
program's icon twice, thinking they didn't do it fast enough the first 
time, so they get two instances.

Such a program would violate 1-3 letters in ACID, depending on how you 
interpret it.

If you've gone to the effort of preventing a second instance from 
running -- not all that hard to do -- now you have another problem which 
is that your program is doomed to forever run as a single instance, or 
face a major redesign when that requirement comes up.

Programs that never grow beyond their initial requirements are so rare 
as to not be worth talking about.  If there's even the slightest 
possibility that multi-user could become a requirement, it would be 
irresponsible to ship the program with this DB design.  Changing it 
later isn't a mere refactoring, it's a wholesale dump-and-translate 
affair.  The longer you put off such major changes, the more expensive 
they get.

To drag this back on topic for this list, you might look over the SSQLS 
v2 design notes in the Wishlist and the URL linked from the first item 
in that section to see if you have some design ideas that would make 
this sort of thing easier.