Programmatically Update an attribute in Core Data

Question

I've looked through all the class documentation for Core Data and I can't find away to programmatically update values in a core data entity. For example, I have a structure similar to this:

 id  | title
============
  1  | Foo  
  2  | Bar  
  3  | FooFoo

Say that I want to update Bar to BarBar, I can't find any way to do this in any of the documentation.

Answer 1

In Core Data, an object is an object is an object - the database isn't a thing you throw commands at.

To update something that is persisted, you recreate it as an object, update it, and save it.

NSError *error = nil;

//This is your NSManagedObject subclass
Books * aBook = nil;

//Set up to get the thing you want to update
NSFetchRequest * request = [[NSFetchRequest alloc] init];
[request setEntity:[NSEntityDescription entityForName:@"MyLibrary" inManagedObjectContext:context]];
[request setPredicate:[NSPredicate predicateWithFormat:@"Title=%@",@"Bar"]];

//Ask for it
aBook = [[context executeFetchRequest:request error:&error] lastObject];
[request release];

if (error) {
//Handle any errors
}

if (!aBook) {
    //Nothing there to update
}

//Update the object
aBook.Title = @"BarBar";

//Save it
error = nil;
if (![context save:&error]) {
           //Handle any error with the saving of the context
}