Hi Gordon,
If you're designing a data model using Core Data, it's actually very
useful to step back and look at your data the way a layperson would.
By this I mean forget about classes and inheritance and all that
stuff. You can come back to it later, but the main thing is to look at
the problem in terms of "I'm trying to model these objects and they
have these properties and interact with each other in these ways." It
turns out that traditional OOP class inheritance and CD entity
inheritance are significantly different. In fact, avoid entity
inheritance unless you know that you will need to do fetches that
return objects of different entity types - otherwise it's just not a
good performance tradeoff.
Given that, could you describe your data in terms that don't impose
specific design choices?
What is the issue in NSManagedObject with regards to calling super?
It's actually recommended that you invoke super for a number of
methods in the class (awakeFromFetch, validateForDelete, and others).
Wil
On Jun 6, 2008, at 5:06 PM, Gordon Apple wrote:
Our data hierarchy has six objects, all of which inherit from
"BaseList"
which contains a dictionary (props) and an array (subList). These
lists are
chained (i.e., the six subclasses). So in the first-attempt data
model,
baselist.sublist is a one-to-many looping back to BaseList.
However, the last item in the chain (Layer) needs it's subList to
point
to shapes instead of BaseList, i.e., subList is now a draw list.
I could
move subList into the subclasses, but there is a lot of recursive
stuff
going on in BaseList where it needs to be. Maybe I could just
override an
accessor so BaseList can get to it. Apparently, there's an issue
calling
"super" in managed objects, so I'll have to see if that poses any
problems.
On Fri, Jun 6, 2008 at 6:59 PM, Gordon Apple <[EMAIL PROTECTED]> wrote:
I'm currently trying to evaluate whether or not Core Data is a
viable
storage system in our application. Although I've been through the
tutorials, Refs, and searches, I still have questions:
1. Our data hierarchy model does not seem to fit into the Core
Data object
model. (At least I haven't been able to make it fit so far). Now
what?
Redo the data model?
This seems unlikely. Can you provide some more information on your
model? You may simply be looking at Core Data the wrong way.
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