iPhone核心数据可以缓存NSManagedObjects吗？

Question

I'm running a data model in one of my apps, where an event has an "eventType" relationship defined. This allows me to modify the look and feel of multiple events by changing their "eventType" relationship object.

The problem that I'm running into is that before I insert an event, I check if a typeRelationship for this object is present with the code below. This takes some time if I need to insert a large number of objects.

Can I cache the results of this fetch request (for example in NSMutableDictionary ) and check that dictionary (local memory) to see if there is an NSManagedObject with the given EventIDEnum ? Can I keep the cache alive forever, or will the underlying objects get "out of date" after a while?

-(Event*)insertAndReturnNewObjectWithTypeID:(EventIDEnum)eventTypeID date:(NSDate*)date
{

    NSFetchRequest *eventTypesArray = [NSFetchRequest fetchRequestWithEntityName:@"EventType"];
    eventTypesArray.predicate = [NSPredicate predicateWithFormat:@"SELF.id == %d", eventTypeID];
    NSArray *eventTypes = [[DataManager sharedInstance].managedObjectContext executeFetchRequest:eventTypesArray error:nil];

    if(eventTypes.count==0)
    {
        DLog(@"ERROR inserting event with type: %i NOT FOUND",(int)eventTypeID);
        return nil;
    }
    else {

        if(eventTypes.count !=1)
        {
            DLog(@"ERROR found %i events with type %i",eventTypes.count,(int)eventTypeID);
        }

        EventType* eventType = [eventTypes lastObject];

        if(date)
        {
//            DLog(@"Returning object");
            return [self insertAndReturnNewObjectWithEventType:eventType date:date];
        }else {
//            DLog(@"Returning object");
            return [self insertAndReturnNewObjectWithEventType:eventType];
        }



    }
}

Thank you for taking a look at my question!

Answer 1

The array of objects returned by a fetch request cannot be cached. They are only valid as long as the NSManagedObjectContext that was used to query them has not been released. The NsManagedObject.objectID and the data you retrieve from the query can be cached and kept for as long as you like. You are probably better off copying the pertinent data and objectIDs into another object you cache and maintain separately from CoreData objects; and releasing the core data array that was returned by the fetch request.

Answer 2

The pattern you're using is often referred to as "find or create": look for an object whose uniquing characteristic matches, return it if it exists, create/populate/return it if it didn't exist.

One thing you can do to speed this up is to do the uniquing outside of Core Data. If it's possible based on your data, perhaps you can iterate over your EventIDEnum values, find the unique values you need to have available, and thus reduce the number of fetches you perform. You'll only search once for each EventIDEnum. As long as you're working within one thread/context, you can cache those.

When I'm writing this kind of code, I find it helpful to pass in the NSManagedObjectContext as a parameter. That allows me to use the find-or-create or bulk insert methods anywhere, either on the main thread or within a private queue/context. That would take the place of your [[DataManager sharedInstance] managedObjecContext] call.