Re: core data app questions - help!
Re: core data app questions - help!
- Subject: Re: core data app questions - help!
- From: mmalc crawford <email@hidden>
- Date: Sat, 1 Sep 2007 15:41:03 -0700
On Sep 1, 2007, at 9:57 AM, Ricardo Strausz wrote:
But the main thing to have in mind is that if you have a good model,
you can fetch (see) your data in many ways, just by free.
This us at best misleading; fetches in general are *not* free -- a
fetch causes Core Data to go back to the persistent store, which is an
expensive operation.
You can certainly fetch your data in many ways, but constructing the
correct fetch request is itself not always conceptually free (i.e. you
have to think about it).
Also, you may have to adjust your interface to.
Well, yes...
As I understand, your model is something like W<<-->S : W<<-->I
(with the obvious meanings).
The easiest part is to put at work your to-many relations: any of
the tutorials that come with the tools will explain (in particular,
see http://developer.apple.com/cocoa/coredatatutorial/index.html )
This explains how to create a "default" interface using bindings.
Like Core Data, bindings are not a beginner technology.
If you're able to create your application solely using drag-and-drop/
point-and-click technologies, then fine. But typically there's more
to it than that and if you don't understand the fundamentals on which
those technologies are based then you're left several levels of
abstraction up in the air with no idea how to progress...
For number one, I would recommend to add an entity with dates, and
with relations W<<-->D, so by clicking in a date you can see only
those objects in W with that date... if this can be done with a
nicer interface (a calendar) will be your research – please let us
know ;^)
It's not clear exactly what this means or how it helps.
For the last, you will have to implement a notification centre that
advise you whenever the table changes, so you can calculate the
needed sum using something like [[table displayedObjects]
@sum(duration)].
Again this is at best misleading -- the precise mechanism used to
propagate change notifications will depend on the application
architecture implemented. Moreover, there is no 'displayedObjects'
method, and you cannot send a @sum(duration) message. *If* you're
using bindings, then you might *bind* the 'value' of a text field to
the sum of duration properties of the *arrangedObjects* in a relevant
array controller.
mmalc_______________________________________________
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