How to update existing object in Core Data? - objective-c

Question

When I insert new object I do with following code:
NSManagedObjectContext *context = [appDelegate managedObjectContext];
Favorits *favorits = [NSEntityDescription insertNewObjectForEntityForName:#"Favorits" inManagedObjectContext:context];
favorits.title = #"Some title";
NSError *error;
if (![context save:&error]) {
NSLog(#"Whoops");
}
How can I update existing object in core data?

Answer 1

Updating is simple as creating a new one.
To update a specific object you need to set up a NSFetchRequest. This class is equivalent to a SELECT statetement in SQL language.
Here a simple example:
NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity:[NSEntityDescription entityForName:#"Favorits" inManagedObjectContext:moc]];
NSError *error = nil;
NSArray *results = [moc executeFetchRequest:request error:&error];
// error handling code
The array results contains all the managed objects contained within the sqlite file. If you want to grab a specific object (or more objects) you need to use a predicate with that request. For example:
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"title == %#", #"Some Title"];
[request setPredicate:predicate];
In this case results contains the objects where title is equal to Some Title. Setting a predicate is equal to put the WHERE clause in a SQL statement.
For further info I suggest you to read the Core Data programming guide and NSFecthRequest class reference.
Core Data Programming Guide
NSFecthRequest Class Reference
Hope it helps.
EDIT (snippet that can be used to update)
// maybe some check before, to be sure results is not empty
Favorits* favoritsGrabbed = [results objectAtIndex:0];
favoritsGrabbed.title = #"My Title";
// save here the context
or if you are not using a NSManagedObject subclass.
// maybe some check before, to be sure results is not empty
NSManagedObject* favoritsGrabbed = [results objectAtIndex:0];
[favoritsGrabbed setValue:#"My title" forKey:#"title"];
// save here the context
In both cases if you do a save on the context, data will be updated.

Answer 2

You have to fetch the object from the context, change the properties you desire, then save the context as you are in your example.

Answer 3

I hope this will help u. as it works for me.
NSMutableArray *results = [[NSMutableArray alloc]init];
int flag=0;
NSPredicate *pred;
if (self.txtCourseNo.text.length > 0) {
pred = [NSPredicate predicateWithFormat:#"courseno CONTAINS[cd] %#", self.txtCourseNo.text];
flag=1;
} else {
flag=0;
NSLog(#"Enter Corect Course number");
}
if (flag == 1) {
NSLog(#"predicate: %#",pred);
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc]initWithEntityName:#"Course"];
[fetchRequest setPredicate:pred];
results = [[self.context executeFetchRequest:fetchRequest error:nil] mutableCopy];
if (results.count > 0) {
NSManagedObject* favoritsGrabbed = [results objectAtIndex:0];
[favoritsGrabbed setValue:self.txtCourseName.text forKey:#"coursename"];
[self.context save:nil];
[self showData];
} else {
NSLog(#"Enter Corect Course number");
}
}

Answer 4

if you are a swift programmer this can help you :
if you want to delete a NSManagedObject
in my case ID is a unique attribute for entity STUDENT
/** for deleting items */
func delete(identifier: String) {
let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
let fetchRequest:NSFetchRequest<NSFetchRequestResult> = NSFetchRequest.init(entityName: "STUDENT")
let predicate = NSPredicate(format: "ID = '\(identifier)'")
fetchRequest.predicate = predicate
do
{
let object = try context.fetch(fetchRequest)
if object.count == 1
{
let objectDelete = object.first as! NSManagedObject
context.delete(objectDelete)
}
}
catch
{
print(error)
}
}
if you want to update a NSManagedObject :
/** for updating items */
func update(identifier: String,name:String) {
let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
let fetchRequest:NSFetchRequest<NSFetchRequestResult> = NSFetchRequest.init(entityName: "STUDENT")
let predicate = NSPredicate(format: "ID = '\(identifier)'")
fetchRequest.predicate = predicate
do
{
let object = try context.fetch(fetchRequest)
if object.count == 1
{
let objectUpdate = object.first as! NSManagedObject
objectUpdate.setValue(name, forKey: "name")
do{
try context.save()
}
catch
{
print(error)
}
}
}
catch
{
print(error)
}
}

Answer 5

I saw an answer in Objective-C which helped me. I am posting an answer for Swift users -
guard let appDelegate = UIApplication.shared.delegate as? AppDelegate else {
return
}
let updateCont = appDelegate?.persistentContainer.viewContext
let pred = NSPredicate(format: "your_Attribute_Name = %#", argumentArray : [your_Arguments])
let request = NSFetchRequest<NSFetchRequestResult>(entityName: "your_Entity_Name")
request.predicate = pred
do {
let resul = try updateCont?.fetch(request) as? [NSManagedObject]
let m = resul?.first
m?.setValue(txtName.text, forKey: "your_Attribute_Name_Whose_Value_Should_Update")
try? updateCont?.save()
} catch let err as NSError {
print(err)
}