core-data

问题 im working with coredata and there is a concept that im not getting; i've 2 managed objects ACConversation and ACMessages with a one to many relationship, so i'm saving a message associated to a conversation and trying to fetch them back based on: NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF.conversation = %@", self.conversation]; but the id associated to the object is different (it seems more a memory address) and with the above predicate it doesnt fetch anything: 2013-01

问题 Firstly, I'm not 100% clued up on Core Data, but I do what I can. So I've implemented Lightweight Migration for when the app is updated, but recently this has failed, i.e. the app crashes after trying to access the local DB. I currently assume that the reason is because of some mix up with the model versions, but even if not so, I think my question is still valid: Is there a way, when updating/upgrading an app, to ignore the Core Data migration process and force the app to use the latest

问题 i have a problem with core data storing integer (i chose int16 because they have a maximum of 6 signs). my model holds Entity: 'Expense' the attribute in question is: @property (nonatomic, retain) NSNumber * month; it was automatically implemented as NSNumber by Xcode (Editor > createManagedmodelsubclass) month holds an short identifier for every month. example 201203 //would be march of 2012 i store new entities with this snippet: [newExpense setValue:monthNumber forKey:@"month"]; which

问题 I have NSManagedObject with properties. Suppose that one property it is: @property (retain, nonatomic) NSString *city; For fetching data form core data I always use NSPredicate . The predicate looks like below: NSPredicate *predicate = [NSPredicate predicateWithFormat:@"%K == %@", @"city", @"San Francisco"]; But the problem here that the project use key "city" as undefined key in meaning like a constant. So lets suppose that I use key "city" in my app 1000 times, so then I need to replace all

问题 i use a combination of queue and resultscontroller to update and display some coredata objects. in my uitableviewcontroller i call every X second a method in my main controller object. [NSTimer scheduledTimerWithTimeInterval:2 target:self selector:@selector(test:) userInfo:nil repeats:YES]; } - (void)test:(NSTimer*)theTimer { [[MainController instance] updatePersons]; } In this method a custom NSOperation object will be added to my main Q. - (BOOL)updatePersons { UpdatePersonsOperation* u = [

问题 I have two managedobjectcontext I fetch object from managedobjectcontext1 and want two save it in the second object context while try to do that I get the error: "Illegal attempt to establish a relationship between objects in different contexts". The code I use NSError * error; NSPersistentStoreCoordinator *persistentStoreCoordinator_OLD; NSPersistentStoreCoordinator *persistentStoreCoordinator_NEW; NSManagedObjectModel *managedObjectModel_OLD; NSManagedObjectModel *managedObjectModel_NEW;

问题 I have two managedobjectcontext I fetch object from managedobjectcontext1 and want two save it in the second object context while try to do that I get the error: "Illegal attempt to establish a relationship between objects in different contexts". The code I use NSError * error; NSPersistentStoreCoordinator *persistentStoreCoordinator_OLD; NSPersistentStoreCoordinator *persistentStoreCoordinator_NEW; NSManagedObjectModel *managedObjectModel_OLD; NSManagedObjectModel *managedObjectModel_NEW;

问题 If I understand correctly, the idea behind Core Data transformable attributes is: implement an NSValueTransformer subclass with returns [NSData class] in +transformedValueClass along with its implementation for transformation register the transformer in +load or +initialize set an entity's attribute as transformable set a name for your transformer (the name you used to register it) in the xcode model editor for the attribute. At this point, I'd expect that accessing or setting the attribute

问题 If I understand correctly, the idea behind Core Data transformable attributes is: implement an NSValueTransformer subclass with returns [NSData class] in +transformedValueClass along with its implementation for transformation register the transformer in +load or +initialize set an entity's attribute as transformable set a name for your transformer (the name you used to register it) in the xcode model editor for the attribute. At this point, I'd expect that accessing or setting the attribute

问题 I have a very simple Core Data demo, in which there is only one button. When I click the 'run' button, the App creates 10,000 objects in a for-loop, which is running in the global queue . Update for more detail : If I put the for-loop in main thread, it runs well. Update for my intent : I know that MOC is not thread-safe, but according to the Apple doc, we can also use serial queue to access the MOC, and the serial queue uses more than one threads. Here I create the Core Data stack: #pragma