Question

I have a fairly simple iPhone app which utilizes CoreData for object persistence.
The object has, amongst other attributes, an NSNumber attribute, defined in the datamodel along with all the other attributes. I set this during the application run cycle to 1 if the user clicks on a particular button. I then call the store function which definitely does get called, and is the same function as persisted everything else, and this seems to work temporarily, in that if I check the value of the attribute on my NSManagedObject it has the correct value, if I retrieve the object from the data store and check it it still has the right value. However if I restart the app, it has not persisted, and so it reverts to the default. I’m getting quite frustrated and have tried various methods of forcing the ManagedObjectContext to persist.

Relevant code:
Persistence code…

- (Area*) storeAreaFavourite:(Area*)a
{
    a = [self storeArea:a];
    NSManagedObjectContext *context = [self.fetchedResultsController managedObjectContext];
        //[context refreshObject:a mergeChanges:YES];
    [context processPendingChanges];
    NSLog(@"Stored area with favourite: %@",([a favourite] != nil ? [a favourite] : [NSNumber numberWithInt: 0]));
    return a;
}

- (Area*) storeArea:(Area*)a
{
    NSError *error = nil;
        // Create a new instance of the entity managed by the fetched results controller.
    NSManagedObjectContext *context = [self.fetchedResultsController managedObjectContext];
    NSFetchRequest* request = [[NSFetchRequest alloc] init];
    NSEntityDescription* entity = [NSEntityDescription entityForName:@"Area" inManagedObjectContext:context];
    NSPredicate* predicate = [NSPredicate predicateWithFormat:@"areaId=%@", [a areaId]];
    [request setEntity:entity];
    [request setPredicate:predicate];
    NSArray* matchedAreas = [context executeFetchRequest:request error:&error];
    if (error != nil)
    {
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
    }
        //NSLog(@"Matched %d Areas", [matchedAreas count]);
    Area* newArea = [matchedAreas count] > 0 ? [matchedAreas objectAtIndex:0] : nil;
    if (newArea == nil)
    {
        newArea = [NSEntityDescription insertNewObjectForEntityForName:@"Area" inManagedObjectContext:context];
    }
    else {
            //NSLog(@"Area: %@ -> %@ ParentArea: %@ -> %@", [newArea valueForKey:@"areaId"], [a areaId], [(Area*)[newArea  valueForKey:@"parentArea"] areaId], [(Area*)[a parentArea] areaId]);
    }


        // If appropriate, configure the new managed object.
    [newArea setValue:[a areaId] forKey:@"areaId"];
    [newArea setValue:[a areaName] forKey:@"areaName"];
    [newArea setValue:[a parentArea] forKey:@"parentArea"];
    [newArea setValue:[a height] forKey:@"height"];
    [newArea setValue:[a width] forKey:@"width"];
    [newArea setValue:[a xPos] forKey:@"xPos"];
    [newArea setValue:[a yPos] forKey:@"yPos"];
    [newArea setValue:[a childAreas] forKey:@"childAreas"];
    [newArea setValue:[a imageName] forKey:@"imageName"];
    [newArea setValue:[a areaText] forKey:@"areaText"];
    [newArea setValue:([a favourite] != nil ? [a favourite] : [NSNumber numberWithInt: 0]) forKey:@"favourite"];
    if ([a favourite] != nil && [[NSNumber numberWithInt:1] isEqualToNumber:[a favourite]])
    {
        NSLog(@"Storing area with areaId: %@",[a areaId]);
        NSLog(@"Storing area with areaName: %@",[a areaName]);
        NSLog(@"Storing area with parentArea: %@",[a parentArea]);
        NSLog(@"Storing area with height: %@",[a height]);
        NSLog(@"Storing area with width: %@",[a width]);
        NSLog(@"Storing area with xPos: %@",[a xPos]);
        NSLog(@"Storing area with yPos: %@",[a yPos]);
        NSLog(@"Storing area with childAreas: %@",[a childAreas]);        
        NSLog(@"Storing area with imageName: %@",[a imageName]);
        NSLog(@"Storing area with areaText: %@",[a areaText]);
        NSLog(@"Storing area with favourite: %@",([a favourite] != nil ? [a favourite] : [NSNumber numberWithInt: 0]));
    }

        // Save the context.
    if (![context save:&error]) {
        /*
         Replace this implementation with code to handle the error appropriately.

         abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development. If it is not possible to recover from the error, display an alert panel that instructs the user to quit the application by pressing the Home button.
         */
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
            //abort();
    }

    matchedAreas = [context executeFetchRequest:request error:&error];
    if (error != nil)
    {
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
    }
        //NSLog(@"Matched %d Areas", [matchedAreas count]);
    newArea = [matchedAreas count] > 0 ? [matchedAreas objectAtIndex:0] : nil;
    if (newArea != nil)
    {
        NSLog(@"StoredFav:%@:%@",[newArea areaId],[newArea favourite]);
    }
    return newArea;
}

Area.m

// 
//  Area.m
//  MappApp
//
//  Created by Matthew Fellows on 27/07/2011.
//

#import "Area.h"


@implementation Area 

@synthesize height;
@synthesize areaId;
@synthesize xPos;
@synthesize areaName;
@synthesize width;
@synthesize areaText;
@synthesize imageName;
@synthesize yPos;
@synthesize childAreas;
@synthesize parentArea;
@synthesize areaImages;
@synthesize favourite;

- (void)addChildAreasObject:(NSManagedObject *)value{
    if (childAreas == nil)
    {
        childAreas = [[NSMutableSet alloc] init];
    }
    [childAreas addObject:value];
}

- (void)addAreaImagesObject:(NSManagedObject *)value{
    if (areaImages == nil)
    {
        areaImages = [[NSMutableSet alloc] init];
    }
    [areaImages addObject:value];
}

@end

Area.h

//
//  Area.h
//  MappApp
//
//  Created by Matthew Fellows on 27/07/2011.
//

#import <CoreData/CoreData.h>


@interface Area :  NSManagedObject  
{
    NSMutableSet* areaImages;
    NSMutableSet* childAreas;
}

@property (nonatomic, retain) NSNumber * height;
@property (nonatomic, retain) NSNumber * areaId;
@property (nonatomic, retain) NSNumber * xPos;
@property (nonatomic, retain) NSString * areaName;
@property (nonatomic, retain) NSNumber * width;
@property (nonatomic, retain) NSString * areaText;
@property (nonatomic, retain) NSString * imageName;
@property (nonatomic, retain) NSNumber * yPos;
@property (nonatomic, retain) NSMutableSet* childAreas;
@property (nonatomic, retain) NSManagedObject * parentArea;
@property (nonatomic, retain) NSMutableSet* areaImages;
@property (nonatomic, retain) NSNumber* favourite;

@end


@interface Area (CoreDataGeneratedAccessors)
- (void)addChildAreasObject:(NSManagedObject *)value;
- (void)removeChildAreasObject:(NSManagedObject *)value;
- (void)addChildAreas:(NSSet *)value;
- (void)removeChildAreas:(NSSet *)value;

- (void)addAreaImagesObject:(NSManagedObject *)value;
- (void)removeAreaImagesObject:(NSManagedObject *)value;
- (void)addAreaImages:(NSSet *)value;
- (void)removeAreaImages:(NSSet *)value;

@end

Answer 1

You have @synthesized your accessors for what are presumably managed object properties. This means they won’t be passing through the correct core data accessors and will not be updating your model properly. @dynamic should be used to tell the compiler that the proper accessors will be available at run time (the core data framework will be providing them).

I think with what you have now you have basically made all of your attributes transient.