how to delete objects in core data - ios

Question

I am trying to understand how core data works.
So I have in my core data 2 entities : Voiture and Garage (yes, i'm french :) )
I can create objects but i can't delete them ! I tried everything…
It would be nice to help me a bit !
here is my code :
#interface dataBaseViewController ()
#property(strong,nonatomic) UIManagedDocument *document;
#property(strong,nonatomic) NSManagedObjectContext *context;
#end
#implementation dataBaseViewController
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a
[self initDocument];
self.context=self.document.managedObjectContext;
}
-(void) initDocument{
//find url
NSFileManager *fileManager = [NSFileManager defaultManager];
NSURL *documentsDirectory=[[fileManager URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] firstObject];
NSString *documentName=#"MyDocument";
NSURL *url= [documentsDirectory URLByAppendingPathComponent:documentName];
//create / open the document
self.document = [[UIManagedDocument alloc] initWithFileURL:url] ;
if ([[NSFileManager defaultManager] fileExistsAtPath:[url path]]) {
[self.document openWithCompletionHandler:^(BOOL success) {
if (success) NSLog(#"doc ouvert");
if (!success) NSLog(#"couldn’t open document at %#", url);
}];
} else {
[self.document saveToURL:url forSaveOperation:UIDocumentSaveForCreating completionHandler:^(BOOL success) {
if (success) NSLog(#"document created");
if (!success) NSLog(#"couldn’t create document at %#", url);
}];
}
}
- (IBAction)ajouterVoiture:(id)sender {
Voiture *nouvelleVoiture =[NSEntityDescription insertNewObjectForEntityForName:#"Voiture" inManagedObjectContext:self.context];
nouvelleVoiture.marque=#"ferreri";
}
- (IBAction)nbVoitures:(id)sender {
NSError *error;
NSFetchRequest *request=[NSFetchRequest fetchRequestWithEntityName:#"Voiture"];
NSLog(#"nombre de voitures : %lu",[self.context countForFetchRequest:request error:&error]);
}
- (IBAction)delete:(id)sender {
[self.context deletedObjects];
NSError *error;
[self.context save:&error];
}
#end

Answer 1

Once you have fetched a managed object, you can delete it from its managed object context by using the deleteObject: method provided by the context.
NSManagedObject *someObject;
[context deleteObject:someObject];
The object will not be removed from the underlying persistent store on disk until the context is saved, using the save: method.

Answer 2

I highly recommend the Magical Record pod. It greatly simplifies boilerplate Core Data operations.
[MagicalRecord saveWithBlockAndWait:^(NSManagedObjectContext *localContext) {
MyEntity *entity = [MyEntity MR_createInContext:localContext];
MyOtherEntity *otherEntity = [MyOtherEntity MR_findFirstByAttribute:#"id" withValue:12345];
entity.attribute1 = #"Foo";
entity.attribute2 = #"Bar";
[otherEntity deleteInContext:localContext];
}];