13.02.13
Creating a Managed Object
Last Updated on 13.02.13
Written by Mike Zriel
How to create a Managed Object in Objective-c
Creating new item manually with code
- (IBAction)createObject:(id)sender { // Button
...
NSManagedObject *myMO = [NSEntityDescription
insertNewObjectForEntityForName:@"Course"
inManagedObjectContext:[self managedObjectContext]];
[myMO setValue:@"Core Data for iOS and OS X" forKey:@"title"]; // Set the Title
[myMO setValue:[NSDate date] forKey:@"releaseDate"]; // Set the current Date
...
Storing the information, this is in AppDelegate.m
- (NSApplicationTerminateReply)applicationShouldTerminate:(NSApplication *)sender
...
NSError *error = nil;
if (![[self managedObjectContext] save:&error]) { // <-- Save to Core Data if did not save show error in NSLog
NSLog(@"Error %@",error);
}
...
Creating Object using Elements
...
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:@"dd MMM yyyy"];
// First Course object
Course *first = (Course *) [NSEntityDescription
insertNewObjectForEntityForName:@"Course"
inManagedObjectContext:[self managedObjectContext]];
first.title = @"Core Data for iOS and OS X";
first.releaseDate = [dateFormatter dateFromString:@"13 Feb 2013"];
...
Course must exist in {filename}.xcdatamodeld and your should have an object Course.h and Course.m file, to create Click on Editor->Create Managed Subclass
Fields of Course are Title and as String and releaseData as date
To get the data you use a Fetch Request as follows
...
// Create fetch Request
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Course" inManagedObjectContext:[self managedObjectContext]];
[fetchRequest setEntity:entity];
// Where
// NSPredicate *where = [NSPredicate predicateWithFormat:@"author==[c] 'Mike Zriel'"]; // not case sensitive equals
// NSPredicate *where = [NSPredicate predicateWithFormat:@"author LIKE[cd] '*vid*'"]; // not case sensitve and accents LIKE * is wildcard
NSPredicate *where = [NSPredicate predicateWithFormat:@"author LIKE[c] 'Mike*' AND releaseDate < %@", [NSDate date]]; // not case sensitive and with parameter Date in this case
[fetchRequest setPredicate:where];
// Sort like order by in sql
NSSortDescriptor *sortDate = [[NSSortDescriptor alloc] initWithKey:@"releaseDate" ascending:YES];
NSSortDescriptor *sortTitle = [[NSSortDescriptor alloc] initWithKey:@"title" ascending:YES];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortTitle,sortDate,nil];
[fetchRequest setSortDescriptors:sortDescriptors];
NSError *error = nil;
NSArray *fetchedObjects = [[self managedObjectContext] executeFetchRequest:fetchRequest error:&error];
if (fetchedObjects == nil) {
NSLog(@"Error: %@",error);
}
// Log the result for testing
for( Course *c in fetchedObjects) { // for each loop
NSLog(@"Title: %@ Author %@ Date: %@",c.title,c.author,c.releaseDate);
}
...
You get get a Sample of this code in the Code Snippet Library {}, search for "core data"
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