[Zope] ObjectManager example needed

[Dylan Reinhardt]

On Tue, 2003-11-25 at 10:19, Paul Winkler wrote:
> On Tue, Nov 25, 2003 at 09:17:03AM -0800, Dylan Reinhardt wrote:
> > Using my data model, let's say Aida has a "piece_composer" property of
> > 'Verdi' and there is a Verdi object in the Composers folder, a peer to
> > the Pieces folder.  To render useful composer information in a Piece
> > object's interface, all you need to do is something like:
> > 
> > -----
> > 
> > <B>Composer</B>:
> >   <dtml-call "REQUEST.set('compsr_obj', _[piece_composer])">
> >   <a href=Composers/<dtml-var "compsr_obj.getId()">
> >   ><dtml-var "compsr_obj.title"></a>
> > -----
> > 
> > And you're done.  Each piece displays its composer and links to the
> > composer detail screen.  Data management is practically transparent.
> 
> The more interesting problem is to find all pieces
> composed by Verdi.

Which is why my original suggestion included caching reverse
references.  

Splitting a pair of "foreign keys" across two objects is not much more
difficult than (or conceptually much different from) storing a pair of
foreign keys in a third table/object.  The important thing is that both
elements of the pair be managed by a *single* set of processes.  If the
process that updates one side is the only process that updates the other
side, you won't have to worry much about orphaned references.  A small
amount of validation can virtually eliminate the problem.

Having a single process strongly implies using an *interface* for
managing references... you don't want to simply expose your references
in a text field. 

I recognize that this practice is unconventional, so I won't go very far
out on a limb defending it.  But it has worked very well for me and this
list is all about sharing stuff that works well.  

> Fortunately, I can give the solution in one word: ZCatalog.

Sure, that works too... primarily by doing something very similar with a
far greater amount of overhead. :-)

Dylan