On 13/02/2006, at 4:09 PM, David Avendasora wrote:
Or maybe your model should have a 'status' field and avoid all
that nasty inheritence altogether. :-)
I probably agree that in this model, a status (state) field would
be better because you are looking at a single item that changes
state over time and that's not a good use of inheritance. But a
misuse of inheritance does not make inheritance nasty - it mostly
works well in EO in all three flavours (apart from a known bug
with flattened).
I and a new OO programmer and I *really* appreciate everyone's
advice on OO design!
In this case, these three part types have some very specific
differences. It is not one part that changes. My application is
being built to manage the manufacturing in a bakery.
- Raw parts are sugar, flour, oil, etc. and are usually procured
from outside vendors.
- Intermediate parts are things like dough, toasted coconut and
such where an intermediate part has a Bill of Materials and
requires work within the manufacturing line to have produced.
- Finished parts things like like cookie, bar, etc. and are parts
made up of any number of Raw and/or Intermediate parts. Since they
are sold to customers they also have to have additional attributes
like UPC code, customer specific attributes.
Does this still sound like something that would work better as an
implementation of the Status Pattern, or should I stick with
Inheritance?
OK, that clarifies it and I think your inheritance design is probably
fine. Do these three kinds of things have features in common? Data
values (either attributes or typed functions) and procedures (untyped
(void) functions). What I do think you'll have is for the
intermediate and final parts, as 'has-a' relationship 'ingredients'.
Make sure you don't mix up the is-a (inheritance) with has-a
(component-of) relationships. Otherwise inheritance is fine.
Ian
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