Question

I am adding object exercise to object session (as a relationship).

In a view, I want to fetch and display exercises for a particular session object.

Right now it is showing all exercises in the database rather than just for that session object.

The relationship between the two objects is called “exercises”.

This is the current code I am using for the fetch if anyone can help me.

    // Create the fetch request for the entity.
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
// Edit the entity name as appropriate.
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Exercise" inManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:entity];

LogResultsViewController *logResultsTableViewController = [[LogResultsViewController alloc]init];
[fetchRequest setPredicate:[NSPredicate predicateWithFormat: @"exercises = %@", logResultsTableViewController.selectedSession]];

// Set the batch size to a suitable number.
[fetchRequest setFetchBatchSize:20];

// Edit the sort key as appropriate.
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];

Updated Code:

- (void) viewDidLoad
{
NSSet *exercises = [self.selectedSession valueForKey:@"exercises"];
NSArray *sortDescriptors = [NSArray arrayWithObject:[NSSortDescriptor sortDescriptorWithKey:@"timeStamp" ascending:YES]];
NSArray *sorted = [exercises sortedArrayUsingDescriptors:sortDescriptors];
sorted = self.exerciseArray;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    return [exerciseArray count];
}

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    return 1;
}

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"Cell";
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil) {
        cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];
    }
    cell.textLabel.text = [exerciseArray objectAtIndex:indexPath.row];
    return cell;
}

When I NSLog the selectedSession, here is what it shows:

selectedSession: <Session: 0x7336940> (entity: Session; id: 0x7334f70 <x-coredata://17D44726-23F7-402F-9CBE-2EED96212E14/Session/p1> ; data: {
exercises = "<relationship fault: 0x5d34680 'exercises'>";
timeStamp = "2011-05-31 04:41:07 +0000";

Also, when I NSLog the NSSset called exercises, I get:
Relationship fault for (<NSRelationshipDescription: 0x711b370>), name exercises, isOptional 1, isTransient 0, entity Session, renamingIdentifier exercises, validation predicates (
), warnings (
), versionHashModifier (null), destination entity Exercise, inverseRelationship exercises, minCount 0, maxCount 0 on 0x7140790

Update:

Ok so I changed the code in cellForRowAtIndex to have
Exercise *exercise = (Exercise *)[exerciseArray objectAtIndex:indexPath.row];
cell.textLabel.text = exercise.name;

Now it shows the exercise name but it is showing the same list of exercises for all sessions, instead of just for the session to which it belongs to.

Answer 1

If your instances of Session have a relationship to instances of Exercise, you don’t need to do another fetch to get the session’s exercises. You can just follow the relationship and get them directly– they’ll be loaded automatically. From your code it looks like logResultsTableViewController.selectedSession is an instance of Session. If that’s the case, you can get all of that session’s exercies as follows (assuming the relationship is called exercises):

NSSet *exercises = [logResultsTableViewController.selectedSession valueForKey:@"exercises"];

You can then sort that NSSet as needed.