R – Does Core Data cache transient attributes

core-dataiphone

I have the following scenario:

entity with a transient attribute used for sectioning
web-based data model periodically refreshed
NSFetchedResultsController

Everything works fine, but when I do a refresh, that transient attribute seems to be getting out of date.

The attribute is returned by an accesssor in my entity object. I tried setting a breakpoint in the accessor, and notice that it's not actually called when my app starts up and my NSFetchedResultsController. This seems to indicate that Core Data is caching this value somewhere (since my table is still section properly). Is there a way to clear this cache?

Best Answer

Yes. Use

+ (void)deleteCacheWithName:(NSString *)name;

The name is the one you provided during NSFetchedResultsController initialization time, when calling

- (id) initWithFetchRequest:(NSFetchRequest *)fetchRequest managedObjectContext:(NSManagedObjectContext *)context sectionNameKeyPath:(NSString *)sectionNameKeyPath cacheName:(NSString *)name;

setting the cacheName argument.

Alternatively, you can avoid Core Data caching the data during NSFetchedResultsController initialization time: simply pass nil for the cacheName argument.

Related Solutions

Iphone – How to properly configure NSFetchedResultsController

I think you still need to tell the NSFetchedResultsController to actually perform the fetch:

NSError *error;
BOOL success = [controller performFetch:&error];

(taken from the example in the NSFetchedResultsController reference)

one other thing that seems odd: do you really want to use "title" as the sectionNameKeyPath? won't that basically create a separate section for each book?

Core Data and transient properties

The problem with setPrimitive... methods is that although NSManagedObject will respond to them at runtime, the compiler has no way of knowing they exist. You can suppress the warning messages by declaring the method in your entity class's header file, using a category so the compiler doesn't yell at you for not defining it in your implementation.

Another option is just using calling [self setPrimitiveValue:value forKey:@"key"]; for each of the attributes you need to access. I've used this method in the past, although I just noticed in the docs that this is discouraged on 10.5 and later.

Best Answer

Related Solutions

Iphone – How to properly configure NSFetchedResultsController

Core Data and transient properties

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