Re: [SQLObject] Using SQLObjects as Abstract Classes

[Brad B. <br...@bb...>]

On Fri, Jul 25, 2003 at 01:19:02PM -0500, Ian Bicking wrote:
> On Fri, 2003-07-25 at 12:27, Brad Bollenbach wrote:
> > > If you have that class layout, you are supposing that there will be
> > > other subclasses of Monitor.  However, each of these subclasses must be
> > > a separate table, or great confusion will ensue.
> > 
> > There will only be a single monitor table. Monitors store a common set
> > of properties. The only thing that's different is how they behave when
> > you say "do your monitor check".
> 
> Then make that into a multiple-class object, Checker.  Like:
> 
> class Checker(object):
>     def __init__(self, monitor):
>         self.monitor = monitor
>     def check(self):
>         assert 0, "Subclass responsibility"
> class HTTPChecker(Checker):
>     def check(self): ...
> class MD5HTTPChecker(HTTPChecker):
>     def check(self): ...
> 
> checkers = {'http': HTTPChecker, 'md5': MD5HTTPChecker}
> 
> class Monitor(SQLObject):
>     monitorType = StringCol(length=10)
>     def _get_checker(self):
>         return checkers[self.monitorType](self)
> 
> 
> Voila!  Composition beats inheritance!

Indeed, this looks like the best way to do it (whilst avoiding any
ugly hacks).

Thanks. :)

--
Brad Bollenbach
BBnet.ca