Objective-C Fundamentals

Building the PocketTasks application
239
important line here is the call to NSEntityDescription’s insertNewObjectForEntity-
ForName:inManagedObjectContext: method. It creates a new Person managed object
and returns it. You can set its values in the next two lines. Notice, however, that this doesn’t
save anything yet! Only the call to save: on managedObjectContext saves the data.
For some extra fun, comment the line that sets either the first or the last name and
build and run again. Notice in the Console that Core Data refuses to save your data
because you defined that both the first and last names are required.
12.4.5 Fetching Person entities in pure code
Naturally, you want access to the data you’ve saved (otherwise, this whole thing would
be pretty pointless, wouldn’t it?). Listing 12.5 shows the implementation of the dump-
DataToConsole method. And it does just that: fetches all Person entities ordered by
the last name and outputs them to the Console. The ordering is accomplished by an
array of NSSortDescriptors (just one, in this case). An instance of NSSortDescriptor
describes how objects should be ordered by setting the name of the property and,
optionally, a method or block that should be used to compare objects and by specifying
whether the order should be ascending or descending. The method setSort-
Descriptors: of NSFetchRequest takes an array of NSSortDescriptors because you
might want to order by last name and then first name, for example.
Listing 12.5
Dumping all Person entities to the Console in
PocketTasksAppDelegate.m
- (void)dumpDataToConsole {
NSManagedObjectContext *moc = [self managedObjectContext];
NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity:[NSEntityDescription entityForName:@"Person"
inManagedObjectContext:moc]];
// Tell the request that the people should be sorted by their last name
[request setSortDescriptors:[NSArray arrayWithObject:
[NSSortDescriptor sortDescriptorWithKey:@"lastName"
ascending:YES]]];
NSError *error = nil;
NSArray *people = [moc executeFetchRequest:request error:&error];
[request release];
}
if (error) {
NSLog(@"Error fetching the person entities: %@", error);
} else {
for (NSManagedObject *person in people) {
NSLog(@"Found: %@ %@", [person valueForKey:@"firstName"],
[person valueForKey:@"lastName"]);
}
}
Finally, you just need to change the application:didFinishLaunchingWith-
Options: method to call the dumpDataToConsole method instead of the create-
SampleData method, as in the following listing.