NSManagedObject's @synthesize attribute stays faulted after modifying a relationship

Question

I'm using code derived from Apple's DateSectionTitles example code. In my class Appointment I have a relationship to Location. Furthermore I generate a section identifier used by a UITableViewController.

@class Location;

@interface Appointment : NSManagedObject

@property (nonatomic, retain) NSDate * begin;
@property (nonatomic, retain) NSDate * end;
@property (nonatomic, retain) Location * location;

@property (nonatomic, retain) NSString *sectionIdentifier;
@property (nonatomic, retain) NSString *primitiveSectionIdentifier;

@end



@implementation Appointment

@synthesize begin = _begin;
@dynamic end;
@dynamic location;
@dynamic primitiveSectionIdentifier;
@dynamic sectionIdentifier;

#pragma mark -
#pragma mark Transient properties

- (NSString *)sectionIdentifier {

    // Create and cache the section identifier on demand.

    [self willAccessValueForKey:@"sectionIdentifier"];
    NSString *tmp = [self primitiveSectionIdentifier];
    [self didAccessValueForKey:@"sectionIdentifier"];

    if (!tmp) {
        /*
         Sections are organized by month and year. Create the section identifier as a string representing the number (year * 1000) + month; this way they will be correctly ordered chronologically regardless of the actual name of the month.
         */
        NSCalendar *calendar = [NSCalendar currentCalendar];

        NSDateComponents *components = [calendar components:(NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit)
                                                   fromDate:[self begin]];
        tmp = [NSString stringWithFormat:@"%d", ([components year] * 10000) + [components month] * 100 + [components day]];
        [self setPrimitiveSectionIdentifier:tmp];
    }

    return tmp;
}


#pragma mark -
#pragma mark Begin setter

- (void)setBegin:(NSDate *)begin
{
    // If the time stamp changes, the section identifier become invalid.
    [self willChangeValueForKey:@"begin"];
    [self willChangeValueForKey:@"primitiveSectionIdentifier"];

    _begin = begin;
    [self setPrimitiveSectionIdentifier:nil];

    [self didChangeValueForKey:@"begin"];
    [self didChangeValueForKey:@"primitiveSectionIdentifier"];
}

@end

---

The problem: After altering the location the data stays faulted. Before modifying location the object looks like this:

<Appointment: 0x837d570> (entity: Appointment; id: 0x837c900 <x-coredata://83B2187C-00B3-4029-B4C5-4EB69C18FC59/Appointment/p1> ; data: {
    begin = "2013-07-27 16:00:00 +0000";
    end = "2013-07-27 18:00:00 +0000";
    location = "0x837e6c0 <x-coredata://83B2187C-00B3-4029-B4C5-4EB69C18FC59/Location/p1>";
})

After altering the property location:

<Appointment: 0x9b7b1f0> (entity: Appointment; id: 0x9b7ab50 <x-coredata://83B2187C-00B3-4029-B4C5-4EB69C18FC59/Appointment/p1> ; data: <fault>)

If I relinquish from generating a section identifier and using a @dynamic instead of a @synthesized property it still works. What's the cause of this and how can I overcome this?

Answer 1

Thanks to Martin R who pointed me in the right direction I've found the problem in my code.

What I didn't know was the fact that Core Data automatically generates additional primitive properties for you:

For example, given an entity with an attribute firstName, Core Data automatically generates firstName, setFirstName:, primitiveFirstName, and setPrimitiveFirstName:. Core Data does this even for entities represented by NSManagedObject. To suppress compiler warnings when you invoke these methods, you should use the Objective-C 2.0 declared properties feature, as described in “Declaration.”

(Source)

The fact that I wasn't aware of this leaded me to adopt the example code in a wrong way. The way it works for me is now:

@class Location;

@interface Appointment : NSManagedObject

@property (nonatomic, retain) NSDate * primitiveBegin;
@property (nonatomic, retain) NSDate * begin;

@property (nonatomic, retain) NSDate * end;
@property (nonatomic, retain) Location * location;

@property (nonatomic, retain) NSString *sectionIdentifier;
@property (nonatomic, retain) NSString *primitiveSectionIdentifier;

@end




@implementation Appointment

@dynamic primitiveBegin;
@dynamic begin;

@dynamic end;
@dynamic location;

@dynamic primitiveSectionIdentifier;
@dynamic sectionIdentifier;


#pragma mark -
#pragma mark Transient properties

- (NSString *)sectionIdentifier {

    // Create and cache the section identifier on demand.

    [self willAccessValueForKey:@"sectionIdentifier"];
    NSString *tmp = [self primitiveSectionIdentifier];
    [self didAccessValueForKey:@"sectionIdentifier"];

    if (!tmp) {
        /*
         Sections are organized by month and year. Create the section identifier as a string representing the number (year * 1000) + month; this way they will be correctly ordered chronologically regardless of the actual name of the month.
         */
        NSCalendar *calendar = [NSCalendar currentCalendar];

        NSDateComponents *components = [calendar components:(NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit)
                                                   fromDate:[self begin]];
        tmp = [NSString stringWithFormat:@"%d", ([components year] * 10000) + [components month] * 100 + [components day]];
        [self setPrimitiveSectionIdentifier:tmp];
    }

    return tmp;
}


#pragma mark -
#pragma mark Begin setter

- (void)setBegin:(NSDate *)begin
{
    // If the time stamp changes, the section identifier become invalid.
    [self willChangeValueForKey:@"begin"];
    [self setPrimitiveBegin:begin];
    [self didChangeValueForKey:@"begin"];

    [self setPrimitiveSectionIdentifier:nil];
}


#pragma mark -
#pragma mark Key path dependencies

+ (NSSet *)keyPathsForValuesAffectingSectionIdentifier
{
    // If the value of timeStamp changes, the section identifier may change as well.
    return [NSSet setWithObject:@"begin"];
}

@end