UIManagedDocument Creation in ViewDidLoad

After some research I am still unsure on when / how I should create my UIManagedDocument.

@interface ViewController ()
@property (strong, nonatomic) UIManagedDocument *document;
@end

@implementation ViewController

- (void) viewWillAppear:(BOOL)animated
{
[super viewWillAppear:YES];

NSFileManager *fileManager = [NSFileManager defaultManager];
NSURL *documentsDirectory = [[fileManager URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] firstObject];
NSString *documentName = @"MyDocument";
NSURL *url = [documentsDirectory URLByAppendingPathComponent:documentName];

BOOL fileExists = [[NSFileManager defaultManager] fileExistsAtPath:[url path]];

if (fileExists) {
    [self.document openWithCompletionHandler:^(BOOL success) {
        NSLog(@"Exsits dont create again");
        if (success) [self documentIsReadyCreateAndObject];
        if (!success) NSLog(@"cound not open document at %@", url);
    }];
}
else {
    // create it
    [self.document saveToURL:url forSaveOperation:UIDocumentSaveForCreating completionHandler:^(BOOL success) {
        NSLog(@"Create it");
        if (success) [self documentIsReadyCreateAndObject];
        if (!success) NSLog(@"cound not create document at %@", url);
    }];
}
}

- (void) documentIsReadyCreateAndObject
{
if (self.document.documentState == UIDocumentStateNormal) {
    NSLog(@"document is ready - create obj");
    Car *demo = [NSEntityDescription insertNewObjectForEntityForName:@"Car" inManagedObjectContext:self.document.managedObjectContext];
    demo.carName = @"xxxxx";
}
else {
    NSLog(@"Not ready to go");
}
}

- (void) fetchAndPrint
{
if (self.document.documentState == UIDocumentStateNormal) {
    NSLog(@"document is ready - print objs");
    NSFetchRequest *request = [[NSFetchRequest alloc]initWithEntityName:@"Car"];
    NSArray *results = [self.document.managedObjectContext executeFetchRequest:request error:nil];

    for (Car *aLog in results) {
        NSLog(@"\nNAME: %@", aLog.carName);
    }
}
else {
    NSLog(@"Not ready to go");
}
}

@end