Re: a few Core Data questions: Predicates and document based app
Re: a few Core Data questions: Predicates and document based app
- Subject: Re: a few Core Data questions: Predicates and document based app
- From: Michael B Johnson <email@hidden>
- Date: Thu, 18 Dec 2008 11:18:10 -0800
On Dec 18, 2008, at 11:04 AM, mmalc Crawford wrote:
On Dec 18, 2008, at 10:47 AM, Michael B Johnson wrote:
I have an entity (let's called it MyThing) that has an optional
parentThing relationship. I'm interested in MyThings that either
don't have their parent set, ("parentThing == NIL") or have their
parent set to themselves ("parentThing == SELF"). Do those
predicate forms sound right?
Yes, for more details see
<http://developer.apple.com/documentation/Cocoa/Conceptual/Predicates/Articles/pUsing.html
> and
<http://developer.apple.com/documentation/Cocoa/Conceptual/CoreData/Articles/cdFetching.html
>
Great, thanks. I had skimmed that, but missed the specific example in
"Using".
My other question is regarding the mundanity of doing a Core Data
document based app version versus an old skool Cocoa one,
especially one that used a file package for document storage.
I'm realizing that I have a lot of state in my document that's
specific to the document (i.e. not application settings).
Normally, these would be instance variables of my NSDocument
subclass that I would load/save as part of my document data.
It seems more Core Dataish, though, to make an NSManagedEntity to
hold these values, and then perhaps cache the values in a property
of the NSManagedDocument subclass as I open up.
It would probably be more appropriate to store this as metadata --
see <http://developer.apple.com/documentation/Cocoa/Conceptual/NSPersistentDocumentTutorial/07_Metadata/chapter_8_section_2.html
> for an example of how to set metadata (this is for Spotlight
metadata, but the same principles apply). That would also cut the
Gordian Granny Knot of your other concerns.
I guess that's my question, though. Why is that a bad thing, to have
three relationships from on entity all pointing to another entity,
which is only pointing to the other entity once?
Trying to gain some deeper understanding...
- wave
mmalc
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