Fetching child objects belongs to parent object & put them in tableView (core-data, relationships)

Question

I have two tableViews, the main one adds the parent object, and when you click on a parent object in the tableView, it takes you to the child tableView, I did the first part successfully, but when it comes to fetching the "RIGHT" child objects I get confused, I way I do it is that I fetch ALL child object, the using enumeration I pick the right ones and put then into a NSSet, but that doesn't work, here's the child object table view.m:

 #import "MinorGoalsTableViewController.h"

 @interface MinorGoalsTableViewController ()

 @end

 @implementation MinorGoalsTableViewController
 @synthesize selectedGoal = _selectedGoal;
 @synthesize fetchedResultsController = _fetchedResultsController;
 @synthesize minorGoalsSet;

 // init with goal (for GTVC)
 - (id) initWithGoal:(Goal *)goal {
if (self = [super init]) {

    _selectedGoal = goal;

}

return self;
 }

 - (id)initWithStyle:(UITableViewStyle)style
 {
self = [super initWithStyle:style];
if (self) {
    // Custom initialization
}
return self;
 }

 - (void)viewDidLoad
 {
[super viewDidLoad];
NSError *error = nil;

// Uncomment the following line to preserve selection between presentations.
// self.clearsSelectionOnViewWillAppear = NO;

// Uncomment the following line to display an Edit button in the navigation bar for this view controller.
// self.navigationItem.rightBarButtonItem = self.editButtonItem;




NSLog(@"Minor Goals in %@ are: %lu", self.selectedGoal.title , (unsigned long)[self.selectedGoal.minorGoal count]);


 //    self.minorGoalsSet = nil;

// initializing minorGoalsSet
self.minorGoalsSet = [[NSMutableSet alloc] init];

// performing fetch
if (![self.fetchedResultsController performFetch:&error]) {
    NSLog(@"Error fetching all minor goals: %@", error);
    abort();
}


// creating NSSet that will carry all selectedGoal minor goals
NSSet *minorGoals = self.selectedGoal.minorGoal;


// creating a loop to add minor goals in minorGoalsSet
// add existing minor goals in selected goal to minorGoalsSet
for (MinorGoal *minor in minorGoals) {
    [minorGoalsSet addObject:minor];
}

NSLog(@"minor goals in set: %lu", (unsigned long) [minorGoalsSet count]);
NSLog(@"minor goals in set2: %lu", (unsigned long) [minorGoals count]);

// setting nav title to selected goal title
self.navigationItem.title = _selectedGoal.title;

// adding "add" button to nav
self.navigationItem.rightBarButtonItem = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAdd target:self action:@selector(addNewMinorGoal)];


 }

 - (void) viewWillDisappear:(BOOL)animated {
self.selectedGoal = nil;
 }


   - (void)didReceiveMemoryWarning
  {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
  }

pragma mark - Table view data source

   - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
  {
return [self.selectedGoal.minorGoal count];
//    id <NSFetchedResultsSectionInfo> secInfo = [[self.fetchedResultsController sections] objectAtIndex:section];
//    return [secInfo numberOfObjects];
  }

 - (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];
}

cell.accessoryType = UITableViewCellAccessoryNone;

// Configure the cell...
MinorGoal *minor = [self.fetchedResultsController objectAtIndexPath:indexPath];

// well see about that later
if ([minorGoalsSet containsObject:minor]) {
    cell.textLabel.text = minor.title;
}

// setting cell's title to minor goal's title
 //    cell.textLabel.text = minor.title;

return cell;
 }

pragma mark - fetched results controller method

 - (NSFetchedResultsController*) fetchedResultsController {
if (_fetchedResultsController != nil) {
    return _fetchedResultsController;
}

// creating fetch request
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
     NSEntityDescription *entity = [NSEntityDescription entityForName:@"MinorGoal"
                                             inManagedObjectContext:self.selectedGoal.managedObjectContext];
[fetchRequest setEntity:entity];

NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"title"
                                                               ascending:NO];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
[fetchRequest setSortDescriptors:sortDescriptors];


// setting _fetchedResultsController
   _fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.selectedGoal.managedObjectContext sectionNameKeyPath:nil cacheName:nil];

// performing fetch
NSError *error = nil;
if (![self.fetchedResultsController performFetch:&error]) {
    NSLog(@"Error fetching minors: %@", error);
}

// returning
return _fetchedResultsController;

    }

pragma mark - Table view delegate

   - (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
 {

 }

 - (void) addNewMinorGoal {

// code to show UIAlertView that will add new minor goal
// creating UIAlertView
    UIAlertView *addMinorGoalAlert = [[UIAlertView alloc] initWithTitle:@"Add Minor Goal" message:@"Minor Goal Title" delegate:self cancelButtonTitle:@"Cancel"      otherButtonTitles:@"Save", nil];

// Adding plain textfield for minor goal title
addMinorGoalAlert.alertViewStyle = UIAlertViewStylePlainTextInput;

// showing UIAlertView
[addMinorGoalAlert show];
}

pragma mark - UIAlertView for Add New Minor Delegation

  - (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex {



      if (buttonIndex == 0) {
          NSLog(@"Adding Minor Goal Canceled!");
     }

      else

     {



    // creating string will carry textField value
    NSString *minorTitle = [[alertView textFieldAtIndex:0]text];





    // creating new minor goal
    MinorGoal *newMinorGoal = [NSEntityDescription
                               insertNewObjectForEntityForName:@"MinorGoal"
                                  inManagedObjectContext:self.selectedGoal.managedObjectContext];




    // setting title of new minor goal
    newMinorGoal.title = minorTitle;




    [self.selectedGoal addMinorGoalObject:newMinorGoal];



    // saving
    NSError *error = nil;
    if (![self.selectedGoal.managedObjectContext save:&error]) {
        NSLog(@"Error saving new minor goal: %@", error);
    }
    NSLog(@"we save %@ to %@ and theres %lu in it", newMinorGoal.title,      self.selectedGoal.title, (unsigned long) [self.selectedGoal.minorGoal count]);


    // fetching
    [self.fetchedResultsController performFetch:&error];


    // reloading tableView data
    [self.tableView reloadData];

   }
  }












 @end

Just tell me the right way to fetch the right child object, and should i put them in a NSSet?

Answer 1

seems like I was doing it the hard way, simply create new array that will hold the child objects.

NSMutableArray *minors = self.selectedGoal.minorGoals.allObjects. 

and when you obtain change or add, do it two times, once to the array, and another time with the "self.selectedGoal.managedObjectContext".

Answer 2

It appears that you are using a NSFetchedResultsController to get ALL MinorGoal instances, but you just want to show the child MinorGoals. If you want to use an NSFetchedResultsController then you need to add a predicate to the fetch so that it only returns the MinorGoals that are children of the selected Goal. Assuming that you have created a relationship between MinorGoal and Goal called "parentGoal":

fetchRequest.predicate = [NSPredicate predicateWithFormat:@"self.parentGoal = %@", self.selectedGoal];

Alternatively, don't us the NSFetchedResultsController and instead use the relationship. You will need to convert the NSSet to an array and sort it as the previous answer.

Answer 3

Store your parent object somewhere in your child view controller, typically it should be like

.h file:

@property (nonactomic, strong) ParentObject *parentObject;

.m file

- (id)initWithObject:(ParentObject *)parent {
…
_parentObject = parent;
…
}

then fetching: (you should have @property (nonatomic, strong) NSFecthedResultsController *fetchedResultController)

- (NSFetchedResultsController*)fetchedResultController {
    if (_fetchedResultController) {
        return _fetchedResultController;
    }

    NSFetchRequest *request = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:NSStringFromClass([ChildObject class])];
    [request setEntity:entity];
    NSSortDescriptor *sortDescription = [NSSortDescriptor sortDescriptorWithKey:@"sortOrder" ascending:YES];
    [request setSortDescriptors:@[sortDescription]];
    request.predicate = [NSPredicate predicateWithFormat:@"(parent == %@)", self.parentObject];
    NSFetchedResultsController *controller = [[NSFetchedResultsController alloc] initWithFetchRequest:request managedObjectContext:[NSManagedObjectContext mainThreadContext] sectionNameKeyPath:nil cacheName:nil];
    controller.delegate = self;
    _fetchedResultController = controller;
    return _fetchedResultController;
}

then implement method

- (void)performFetch {
    NSError *error = nil;
    [self.fetchedResultController performFetch:&error];
    if (![self.fetchedResultController performFetch:&error]) {
        [self showAlertWithError:error];
    }
    else {
        [self.tableView reloadData];
    }
}

thats it basically you will receive all child objects you need sorted and filtered by predicate