[Zope] object instances as meta_data in ZCatalogs?

[dee900@anusf.anu.edu.au]

ZCatalog searches return "pluggable brain" instances
rather than the catalogued object.  You've got quick
access to the catalogued meta_data, but if you want
more then you've got to "wake up" the actual object -
and there's a significant performance hit for doing
so.

Consider the following pared-down scenario:

You set up a beautiful ZClass called Point.  Point
has two float properties, x and y.  Point has a method
"distance_to(test_point)" which returns the cartesian
distance from itself to another Point instance (test_point).

Now you catalog all your Point instances and conduct a 
search which returns a list of pluggable brains.  You 
want to quickly find the distance from a given test point 
to each of the points returned by the search:

1) You wake up each object and call 
       "distance_to(test_point)"
   for each.  Clean but performance hit for waking up.
   
2) You add x and y as meta_data, rewrite the method
   distance_to(test_point) as distance_to(x,y).  Now
   you no longer have to wake up each point as the x
   and y are quickly available in the pluggable brain.
   It's quicker but less object-oriented.  Starts to look
   a little like old C code - distance_to(x1,y1,x2,y2).
   Further, it becomes a real mess when your "distance_to"
   calculation uses many properties in addition to x and y.

Is there an alternative that I'm missing?  Ideally you'd
like to have object instances as meta_data in the catalog.
Comments?

Cheers,
Darran.






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