Question

I store data using the following method

- (NSManagedObject *) createCourseWithCourseCode:(NSString *) courseCode {
     NSManagedObject *course = [NSEntityDescription insertNewObjectForEntityForName:@"Course"   inManagedObjectContext:context];
    [course setValue:courseCode forKey:@"CourseCode"];
    [self saveChanges];
    return course;
}

And then I tried to delete with this code, where I am getting the NSManagedObject from a fetch method, but this is not working. ‘An NSManagedObjectContext cannot delete objects in other contexts.’

- (void) removeCourseWithCourseCode:(NSManagedObject *) courseCode {
    [context deleteObject:courseCode];
    [self saveChanges];
}

I was wondering if I could simply delete the object by finding where the key CourseCode matches a string?

Answer 1

You can do this by passing the object’s objectID instead of the actual object.

Your code would look like this:

- (void) removeCourseWithCourseCode:(NSManagedObjectID *) courseCode {
    [context deleteObject:[context existingObjectWithID:courseCode] error:nil];
    [self saveChanges];
}

And you can access an NSManagedObject‘s ID like this:

[someObject objectID];

So your first block of code should look something like this:

- (NSManagedObjectID *) createCourseWithCourseCode:(NSString *) courseCode {
     NSManagedObject *course = [NSEntityDescription insertNewObjectForEntityForName:@"Course"   inManagedObjectContext:context];
    [course setValue:courseCode forKey:@"CourseCode"];
    [self saveChanges];
    return [course objectID];
}