Updating a managedObject in Core Data - objective-c

Question

WHAT I HAVE SO FAR:
In one splitview, I have a a tableview as its master, and a UIView as the detail. The tableview has 2 columns: "Days" and then "Sessions". I get the data from the Core Data, the entities called "Sessions". When I click on a "Session" tableviewcell, the detailview gets updated.
In the detailview, I added an "Add" button in the navigation bar. When you click on this, I add a new entity called "NewSession" to the core data.
if ([_sessionData.added isEqualToNumber:[NSNumber numberWithBool:NO]]) {
[_sessionData setValue:[NSNumber numberWithBool:YES] forKey:#"added"];
SessionData *session = (SessionData*) [NSEntityDescription insertNewObjectForEntityForName:#"NewSessions" inManagedObjectContext:[DataSingleton sharedMySingleton].managedObjectContext];
session.startDate = _sessionData.startDate;
session.endDate = _sessionData.endDate;
session.sessionLocation = nil;
session.sessionTitle = _sessionData.sessionTitle;
session.sessionDescription = _sessionData.sessionDescription;
[session setValue: [NSNumber numberWithBool:YES] forKey:#"added"];
_addButton = [[[UIBarButtonItem alloc] initWithTitle:#"Remove" style:UIBarButtonSystemItemAdd target:self action:nil] autorelease];
NSError *error = nil;
if (![[DataSingleton sharedMySingleton].managedObjectContext save:&error]) {
DebugLog(#"Whoops, couldn't save:%#", [error localizedDescription]);
}
}
else {
NSLog(#"SESSION ALREADY ADDED");
}
ANOTHER splitview's tableview fetches the "NewSession" entity, and gets all the data and displays it.
THE PROBLEM:
Whenever I exit the application and relaunch it, the sessions in the other splitview are still there, BUT I can add the SAME session again.
In the "add" code, I have the following:
[_sessionData setValue:[NSNumber numberWithBool:YES] forKey:#"added"];
Now, my sessionData is an NSManagedObject; and I thought that just setting the values will update them in the core data.
Can anyone help?

Answer 1

I had similar problem, but similar doesn't mean the same. I don't know if it works for you but you can try it. This method was described to me by #macbirdie and it works for me.
First of all, import your AppDelegate header file:
#import "YourAppDelegate.h"
Then, update your code:
if ([_sessionData.added isEqualToNumber:[NSNumber numberWithBool:NO]]) {
[_sessionData setValue:[NSNumber numberWithBool:YES] forKey:#"added"];
NSManagedObjectContext *moc = [[DataSingleton sharedMySingleton] managedObjectContext];
SessionData *session = (SessionData*) [NSEntityDescription insertNewObjectForEntityForName:#"NewSessions" inManagedObjectContext:moc];
session.startDate = _sessionData.startDate;
session.endDate = _sessionData.endDate;
session.sessionLocation = nil;
session.sessionTitle = _sessionData.sessionTitle;
session.sessionDescription = _sessionData.sessionDescription;
session.added = [NSNumber numberWithBool:YES];
_addButton = [[[UIBarButtonItem alloc] initWithTitle:#"Remove" style:UIBarButtonSystemItemAdd target:self action:nil] autorelease];
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(saveMoc:) name:NSManagedObjectContextDidSaveNotification object:moc];
NSError *error = nil;
if (![moc save:&error]) {
DebugLog(#"Whoops, couldn't save:%#", [error localizedDescription]);
}
} else {
NSLog(#"SESSION ALREADY ADDED");
}
And add this methode somewhere in your file:
- (void)saveMoc:(NSNotification *)notification {
YourAppDelegate *appDel = (YourAppDelegate *)[[UIApplication sharedApplication] delegate];
[appDel.managedObjectContext mergeChangesFromContextDidSaveNotification:notification];
}