Re: Object Identity Tests in Core Data
Re: Object Identity Tests in Core Data
- Subject: Re: Object Identity Tests in Core Data
- From: mmalcolm crawford <email@hidden>
- Date: Wed, 31 Aug 2005 02:23:15 -0700
On Aug 31, 2005, at 2:10 AM, Niko Matsakis wrote:
I guess it's that I didn't find documentation on what kinds of
types are available in predicates.
<http://developer.apple.com/documentation/Cocoa/Conceptual/
CoreData/Articles/cdFetching.html#//apple_ref/doc/uid/TP40002484/
DontLinkElementID_18>
Yes, I read this before I posted, and also the Predicate
Programming Guide. To be honest, the section here on comparing to
self left me more confused then when I started.
What really confused me was this line in the code example under
Retrieving Specific objects:
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"self
== %@", targetObject];
In case anyone cares, this is what went though my head after
reading this:
1. Okay, does this mean there is a special property called "self"
on every managed object?
<http://developer.apple.com/documentation/Cocoa/Conceptual/Predicates/
Articles/pSyntax.html#//apple_ref/doc/uid/TP40001795-215930>
"SELF
Represents the object being evaluated."
2. I was confused because I didn't know what type targetObject
was. If it's an NSManagedObject*, which makes sense, then why are
you doing the fetch? You already have the answer!
To make sure that the object is accessible from the specified context.
3. Why is it using string substitution?
It's not string substitution:
<http://developer.apple.com/documentation/Cocoa/Conceptual/Predicates/
Articles/pSyntax.html#//apple_ref/doc/uid/TP40001795/
DontLinkElementID_6>
"The format string supports printf-style format arguments such as %x
(see Formatting String Objects)). Two important arguments are %@ and %K.
%@ is a var arg substitution for a value (usually a string value)."
4. Then it mentions the IN operator, but doesn't show an example.
<http://developer.apple.com/documentation/Cocoa/Conceptual/Predicates/
Articles/pUsing.html#//apple_ref/doc/uid/TP40001794-250111>
mmalc
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