Question

Inside my user object I have the following code to generate a new ‘session’ or continue the existing session if one exists.

Strangely it will keep other properties but just loses the ‘user’ property… user is in a one to many relationship with session, 1 user can have many sessions. (or will do, for the following test I am simply checking for any previous session and using it if it exists)

-(void)setupSessionStuff
{
// Create new Core Data request
NSFetchRequest *request = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Session" inManagedObjectContext:[self managedObjectContext]];
[request setEntity:entity];

// Create Sort Descriptors for request
NSSortDescriptor *startTimeSort = [[NSSortDescriptor alloc] initWithKey:@"startTime" ascending:NO selector:nil];
[request setSortDescriptors:[NSArray arrayWithObjects:startTimeSort, nil]];
[startTimeSort release];

[request setFetchLimit:1]; // Only get the most recent session

// Execute request
NSError *error = nil;
NSArray *results = [[self managedObjectContext] executeFetchRequest:request error:&error];
if (results == nil) {
    // Something went horribly wrong...
    NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
    exit(-1);
}
[request release];

Session *theSession = nil;

if ([results count] == 1) {
    NSLog(@"existing session");
    // Use existing Session
    theSession = [results objectAtIndex:0];

    NSLog(@"session.user: %@", [theSession valueForKey:@"user"]); // this is always null!

} else {
    NSLog(@"new session");
    // Create new Sesson
    theSession = (Session *)[NSEntityDescription insertNewObjectForEntityForName:@"Session" inManagedObjectContext:[self managedObjectContext]];

    // Add the Session to the User
    NSLog(@"before: session.user: %@", theSession.user); // null
    theSession.user = self;
    NSLog(@"after: session.user: %@", theSession.user); // looks good
}

...


NSLog(@"before.save: session.user: %@", theSession.user); // good

// Save everything
error = nil;
if (![[self managedObjectContext] save:&error]) {
    // Something went horribly wrong...
    NSLog(@"Unresolved error: %@, %@, %@", error, [error userInfo],[error localizedDescription]);
    exit(-1);
}

NSLog(@"after.save: session.user: %@", theSession.user); // still there..
}

Additionally I have opened up the Core Data sqlite file and examined with SQLite Manager. It looks like the relationship has been correctly saved, as I can see the userID stored in the session table.

–

Just added this at the start of my method as another test.

NSSet *set = self.session;

for(Session *sess in set) {
    NSLog(@"startTime %@", sess.startTime);
    NSLog(@"user %@", sess.user);

}

Strangely enough the user is set in this case!? So set here then not set a few lines later when I do the fetch request… ?

–

In response to feedback below

Have added this code after assigning session.user = self and both return the expected output. So it does look like the problem is with the subsequent fetch.

NSLog(@"self.session: %@", self.session);
NSLog(@"self.session: %@", [self valueForKey:@"session"]);

Also I agree that accessing my session’s through self.session will let me work around my issue, but it doesn’t solve what is going on here.
In other places I surely won’t be able to walk from one entity to the other so need to confidence the fetch is going to pull everything in correctly.

Answer 1

Well I found the problem and solved my issue…

After examining the memory address of my session entity I noticing that it was changing between runs. Investigating further I discovered that where I had been testing some code earlier in another class, creating a new session entity, but not saving it, well, it was being saved after all – when I issued the save in my code above!