I have this book about Core Data. I am on my second chapter and there’s an ongoing project that I followed. The project adds an Organization, and three employees. One of the employee is a leader. I have successfully followed the steps, although there are 4 warnings but it doesn’t have an error. I know this should work because I had this same project before I reinstall my OSX.
AppDelegate.h
#import <UIKit/UIKit.h>
#import <CoreData/CoreData.h>
@class ViewController;
@interface AppDelegate : UIResponder <UIApplicationDelegate>
@property (strong, nonatomic) UIWindow *window;
@property (strong, nonatomic) ViewController *viewController;
//Core Data Implementation
@property (readonly, strong, nonatomic) NSManagedObjectContext *managedObjectContext;
@property (readonly, strong, nonatomic) NSManagedObjectModel *managedObjectModel;
@property (readonly, strong, nonatomic) NSPersistentStoreCoordinator *persistentStoreCoordinator;
- (void)saveContext;
- (NSURL *)applicationDocumentsDirectory;
//Display Person
- (void)readData;
- (void)displayPerson:(NSManagedObject *)person withIndentation:(NSString *)indentation;
@end
AppDelegate.m
#import "AppDelegate.h"
#import "ViewController.h"
@implementation AppDelegate
@synthesize managedObjectContext = _managedObjectContext;
@synthesize managedObjectModel = _managedObjectModel;
@synthesize persistentStoreCoordinator = _persistentStoreCoordinator;
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
[self createData];
self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
self.viewController = [[ViewController alloc] initWithNibName:@"ViewController" bundle:nil];
self.window.rootViewController = self.viewController;
[self.window makeKeyAndVisible];
return YES;
}
#pragma mark - Create Data
-(void)createData
{
NSManagedObject *organization = [NSEntityDescription insertNewObjectForEntityForName:@"Organization" inManagedObjectContext:self.managedObjectContext];
[organization setValue:@"Company, Inc." forKey:@"name"];
[organization setValue:[NSNumber numberWithInt:[@"Company, Inc." hash]] forKey:@"id"];
NSManagedObject *john = [NSEntityDescription insertNewObjectForEntityForName:@"Person" inManagedObjectContext:self.managedObjectContext];
[john setValue:@"John" forKey:@"name"];
[john setValue:[NSNumber numberWithInt:[@"John" hash]] forKey:@"id"];
NSManagedObject *jane = [NSEntityDescription insertNewObjectForEntityForName:@"Person" inManagedObjectContext:self.managedObjectContext];
[jane setValue:@"Jane" forKey:@"name"];
[jane setValue:[NSNumber numberWithInt:[@"Jane" hash]] forKey:@"id"];
NSManagedObject *bill = [NSEntityDescription insertNewObjectForEntityForName:@"Person" inManagedObjectContext:self.managedObjectContext];
[bill setValue:@"Bill" forKey:@"name"];
[bill setValue:[NSNumber numberWithInt:[@"Bill" hash]] forKey:@"id"];
NSMutableSet *johnsEmployees = [john mutableSetValueForKey:@"employees"];
[johnsEmployees addObject:jane];
[johnsEmployees addObject:bill];
}
- (void)saveContext {
NSError *error = nil;
NSManagedObjectContext *managedObjectContext = self.managedObjectContext;
if (managedObjectContext != nil) {
if ([managedObjectContext hasChanges] && ![managedObjectContext save:&error]) {
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
abort();
}
}
}
#pragma mark - Core Data stack
- (NSManagedObjectContext *)managedObjectContext {
if (_managedObjectContext != nil) {
return _managedObjectContext;
}
NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
if (coordinator != nil) {
_managedObjectContext = [[NSManagedObjectContext alloc] init];
[_managedObjectContext setPersistentStoreCoordinator:coordinator];
}
return _managedObjectContext;
}
- (NSManagedObjectModel *)managedObjectModel {
if (_managedObjectModel != nil) {
return _managedObjectModel;
}
NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"Core01" withExtension:@"momd"];
_managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
return _managedObjectModel;
}
- (NSPersistentStoreCoordinator *)persistentStoreCoordinator {
if (_persistentStoreCoordinator != nil) {
return _persistentStoreCoordinator;
}
NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"Core01.sqlite"];
NSError *error = nil;
_persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];
if (![_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error]) {
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
abort();
}
return _persistentStoreCoordinator;
}
#pragma mark - Application's Documents directory
- (NSURL *)applicationDocumentsDirectory
{
return [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
}
#pragma mark - Display Person
- (void)displayPerson:(NSManagedObject*)person withIndentation:(NSString*)indentation {
NSLog(@"%@Name: %@", indentation, [person valueForKey:@"name"]);
indentation = [NSString stringWithFormat:@"%@ ", indentation];
NSSet *employees = [person valueForKey:@"employees"];
id employee;
NSEnumerator *it = [employees objectEnumerator];
while ((employee = [it nextObject]) != nil) {
[self displayPerson:employee withIndentation:indentation];
}
}
- (void)readData {
NSManagedObjectContext *context = [self managedObjectContext];
NSEntityDescription *orgEntity = [NSEntityDescription entityForName:@"Organization" inManagedObjectContext:context];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
[fetchRequest setEntity:orgEntity];
NSArray *organizations = [context executeFetchRequest:fetchRequest error:nil];
id organization;
NSEnumerator *it = [organizations objectEnumerator];
while ((organization = [it nextObject]) != nil) {
NSLog(@"Organization: %@", [organization valueForKey:@"name"]);
NSManagedObject *leader = [organization valueForKey:@"leader"];
[self displayPerson:leader withIndentation:@" "];
}
}
- (void)applicationWillResignActive:(UIApplication *)application
{
// Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
// Use this method to pause ongoing tasks, disable timers, and throttle down OpenGL ES frame rates. Games should use this method to pause the game.
}
- (void)applicationDidEnterBackground:(UIApplication *)application
{
// Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later.
// If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.
}
- (void)applicationWillEnterForeground:(UIApplication *)application
{
// Called as part of the transition from the background to the inactive state; here you can undo many of the changes made on entering the background.
}
- (void)applicationDidBecomeActive:(UIApplication *)application
{
// Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
}
- (void)applicationWillTerminate:(UIApplication *)application
{
// Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.
}
@end
These are the only codes that are important to the project. Yes, this is a very simple Core Data app.
There’s a guide in the book to access the database by using sqlite3.
In Terminal.app:
Input: cd ~/Library/Application\ Support/iPhone\ Simulator
Input: find . -name "Core01.sqlite" –print
Output: ./6.0/Applications/25DB9FAD-6921-4791-9409-FF84F275D8A8/Documents/Core01.sqlite
Input: sqlite3 ./6.0/Applications/25DB9FAD-6921-4791-9409-FF84F275D8A8/Documents/Core01.sqlite
In sqlite3:
Input: sqlite> select Z_PK, ZID, ZLEADER, ZNAME from ZORGANIZATION;
Output: 1|-19904|2|Company, Inc.
Input: sqlite> select Z_PK, ZID, Z2EMPLOYEES, ZNAME from ZPERSON;
Output:
1|6050|2|Jane
2|-28989||John
3|28151|2|Bill
The problem is, the database is empty. Idk what went wrong, nor what I miss.
I think the problem is that you need to call the method
-(void)saveContextafter you set all the data in-(void)createDataTry this: