[Gambas-user] 38 different classes - all exactly the same.

[Bruce]

As usual this is hard to explain in a short message, but here goes.

We have a major library that provides all the persistence mechanisms for
what we call "Business Objects".  In our case it's Horses, Stables,
Auctions, Trainers, Owners, etc etc, currently 38 of them and growing.
The reason for this is that the database design changes incrementally on
a frequent basis when one of the clients comes up with another good
idea. With 166 different applications to support, it makes sense to cope
with data changes in one central library.

I have been trying to abstract a lot of the methods in the library
classes and have got to the point where the majority of the common logic
is contained in two major classes, and its all driven by metadata "maps"
that relate the BO attributes to the relevant columns and tables in the
database (and vice versa).

The roadblock I have now struck is this.  Each BO class requires a
special "partner class" that contains the metadata as a static
attribute. Each of these classes now looks exactly the same, same data
items, same code.  The only difference is the class name.  Thus, 38
different classes - all exactly the same.  But at runtime, obviously,
each has a different metadata map loaded.

What I'd like to be able to do is have only one of these, rather than
38.

The reason that the metadata is held as a static attribute is that
during any execution of a given program, there might be hundreds
(sometimes thousands) of, say, Horse objects created.  So it makes sense
to only load the metadata once and share it amongst all the BO's of that
type.

So, is there some way to create a class i.e. a new class not a new
object, based on that common code at runtime?   

I have attached a picture that I hope might help in understanding where
I'm coming from.  It's the brown classes inside the pinkish box. 

I've tried looking at design patterns for something like this but really
can't find anything that seems to match.

regards
Bruce
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