CoreData Edit/Overwrite Object

Question

I am playing around with a new project, a split view iPad app using Core Data, and I was wondering, as its fairly clear how to add and remove an item. If I

Answer 1

http://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/CoreData/Articles/cdFetching.html will show you how to fetch an entity,

http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/CoreData/Articles/cdUsingMOs.html will show you how to change properties, and save them.

core data is something where you really want to read a lot of the apple documentation and become familiar, it will save you hours in the long run. hope this helps!

Answer 2

You simply request the existing object using an NSFetchRequest, change whatever fields need to be updated (a simple myObject.propertyName setter is all that's required), and then perform a save action on the data context.

EDIT to add code example. I agree with MCannon, Core Data is definitely worth reading up about.

This code assumes you created the project with a template that includes Core Data stuff, such that your app delegate has a managed object context, etc. Note that there is NO error checking here, this is just basic code.

Fetching the object

// Retrieve the context
if (managedObjectContext == nil) {
    managedObjectContext = [(YourAppNameAppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext];
}

// Retrieve the entity from the local store -- much like a table in a database
NSEntityDescription *entity = [NSEntityDescription entityForName:@"YourEntityName" inManagedObjectContext:managedObjectContext];
NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity:entity];

// Set the predicate -- much like a WHERE statement in a SQL database
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"YourIdentifyingObjectProperty == %@", yourIdentifyingQualifier];
[request setPredicate:predicate];

// Set the sorting -- mandatory, even if you're fetching a single record/object
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"yourIdentifyingQualifier" ascending:YES];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
[request setSortDescriptors:sortDescriptors];
[sortDescriptors release]; sortDescriptors = nil;
[sortDescriptor release]; sortDescriptor = nil;

// Request the data -- NOTE, this assumes only one match, that 
// yourIdentifyingQualifier is unique. It just grabs the first object in the array. 
YourEntityName *thisYourEntityName = [[managedObjectContext executeFetchRequest:request error:&error] objectAtIndex:0];
[request release]; request = nil;

Update the object

thisYourEntityName.ExampleNSStringAttributeName = @"The new value";
thisYourEntityName.ExampleNSDateAttributeName = [NSDate date];

Save the change

NSError *error;
[self.managedObjectContext save:&error];

Now your object/row is updated.