对核心数据对象的更改未持久

Question

I have to NSManagedObjects in core data called Person and Goal. They have a many-to-many relationship. I have a table view controller that shows the Goal objects associated with a given Person object. The purpose of this tableview controller is to allow you to tap a "plus" button inside a given Goal cell and have "points" transferred from the Person object to the Goal object.

The fetch request used to do this is:

NSManagedObjectContext *context = self.context;

if (self.selectedItemID) {
NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Goal"];
request.sortDescriptors = [NSArray arrayWithObjects:
                               [NSSortDescriptor sortDescriptorWithKey:@"name"
                                                             ascending:YES],
                               nil];

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(self IN %@) AND (completed     == %@)",
                      person.goals,
                      [NSNumber numberWithBool:NO]];

if (predicate) [request setPredicate:predicate];

//Note: |self.frc| is defined in the super class
self.frc = [[NSFetchedResultsController alloc] initWithFetchRequest:request
                                                   managedObjectContext:context
                                                     sectionNameKeyPath:nil
                                                              cacheName:nil];
self.frc.delegate = self;

This is the method called by the "Plus" button in each Goal cell:

- (IBAction)modifyPointsForGoal:(UIButton *)sender {

//Get a reference to the |Goal| object for the button's cell.  The view hierarchy may not be fixed,
//so traverse up the view hierarchy until a UITableViewCell is found and get its NSIndexPath

UIView *view = sender;
while (![view isKindOfClass:[GoalForPersonCell class]]) view = view.superview;
GoalForPersonCell *cell = (GoalForPersonCell *)view;
NSIndexPath *indexPath = [self.tableView indexPathForCell:cell];

//Get reference to |Goal| and |Person| object
Goal *cellsGoal = (Goal *)[self.frc objectAtIndexPath:indexPath];
NSManagedObjectID *cellsGoalObjectID = cellsGoal.objectID;
Goal *goal = (Goal *)[self.context existingObjectWithID:cellsGoalObjectID
                                                    error:nil];

Person *person = self.person;


//Using the button tag numbers, increment/decrement values as needed
gFPVCSenderButtonType buttonType = (int)sender.tag;
switch (buttonType) {
    case giveAdd:
        [goal incrementValueBalanceWithDefaults];
        break;

    case giveSubtract:
        [goal decrementValueBalanceWithDefaults];
        break;

    case bankAdd:
        // decrementBalanceForGoalType returns FALSE if there are insufficient funds
        if ([person decrementBalanceUsingGoal:goal])
            [goal incrementValueBalanceWithDefaults];
        break;

    case bankSubtract:
        // decrementValueBalance returns FALSE if there are insufficient funds
        if ([goal decrementValueBalanceWithDefaults])
            [person incrementBalanceUsingGoal:goal];
        break;

    default:
        break;
}

}

The buttons in each cell work as expected - values are taken from the Person object and given to the Goal object represented by the cell. The problem I'm having is that changes to the Person object are written to the persistent store, but changes to the Goal object are not. So, when the app is restarted the Goal object(s) appear to be unchanged.

I've used a SQL browser to verify the changes aren't being written to disk. The changes to the Goal objects are visible if you view the Goal object in other VCs BEFORE closing the app - its as though the changes to the Goal object are written to the context, but again they don't persist, and only for that specific object.

I tried using XCode to regenerate the NSManagedObject subclasses and it didn't resolve the issue. I'm completely stumped, and after seven hours of trying to figure it out I'm at my wits end.

Answer 1

Save changes into persistent store:

NSError *err= nil;
[managedObjectContext save:&err];

Manage your FRC after creating (use once):

    [FRC setAutomaticallyPreparesContent:<#(BOOL)#>];
    [RFC setAutomaticallyRearrangesObjects:<#(BOOL)#>];

Answer 2

It ends up the issue was with my NSManagedObject subclass for the entity.

Rather than add custom methods to the NSManaged sublass created by Xcode from my data model, I used a technique whereas I created the NSManagedObject subclass using XCode and then subclassed it again to add my custom methods. I did this because it allows you to change the entity and re-create the NSManagedObject subclass using XCode without clobbering all the custom methods you wrote.

It also allowed me to do something bad:

_Goal.m

#import "_Goal.h"
@implementation _Goal

@dynamic moneyBalance;
@end

Goal.h

#import "Goal.h"
@end

Goal.m

@synthesize moneyBalance = _moneyBalance

-(NSManagedObject *)setMoneyBalance {
//Custom setter code for boundry checking
}

Because I subclassed things the way I did, the compiler didn't throw an error/warning telling me that I was essentially redefining (in this case overriding) the moneyBalance property by @synthesizing it. This allowed my custom methods to work, but made changes invisible to CoreData.

Once I removed the @synthesize and custom setters, everything worked again.