Coredata错误"data:<fault>"

Question

我尝试使用以下代码从CoreData中提取数据

NSFetchRequest *request = [[NSFetchRequest alloc] init];
request.entity = [NSEntityDescription entityForName:@"Cave" inManagedObjectContext:self.context];
request.predicate = [NSPredicate predicateWithFormat:@"(latitude > 0) AND (longitude > 0)"];

NSError *error;
NSLog(@"%@",[self.context executeFetchRequest:request error:&error]);
NSLog(@"%@",[error localizedDescription]);

CoreData应该有9个匹配的对象,它会找到9个对象.所以谓词应该可以工作,但我在控制台中得到了这个

2011-09-05 07:41:42.267 CaveConditions[6930:11903] (
    "<NSManagedObject: 0x7368060> (entity: Cave; id: 0x7367880 <x-coredata://C825FC9D-3490-4D8A-A811-979B819A2EB6/Cave/p31> ; data: <fault>)",
    "<NSManagedObject: 0x73547e0> (entity: Cave; id: 0x7356e20 <x-coredata://C825FC9D-3490-4D8A-A811-979B819A2EB6/Cave/p40> ; data: <fault>)",
    "<NSManagedObject: 0x73681e0> (entity: Cave; id: 0x7363e60 <x-coredata://C825FC9D-3490-4D8A-A811-979B819A2EB6/Cave/p42> ; data: <fault>)",
    "<NSManagedObject: 0x7368280> (entity: Cave; id: 0x7356be0 <x-coredata://C825FC9D-3490-4D8A-A811-979B819A2EB6/Cave/p72> ; data: <fault>)",
    "<NSManagedObject: 0x7368320> (entity: Cave; id: 0x733ad80 <x-coredata://C825FC9D-3490-4D8A-A811-979B819A2EB6/Cave/p73> ; data: <fault>)",
    "<NSManagedObject: 0x73683c0> (entity: Cave; id: 0x7333e70 <x-coredata://C825FC9D-3490-4D8A-A811-979B819A2EB6/Cave/p91> ; data: <fault>)",
    "<NSManagedObject: 0x7368480> (entity: Cave; id: 0x7361810 <x-coredata://C825FC9D-3490-4D8A-A811-979B819A2EB6/Cave/p101> ; data: <fault>)",
    "<NSManagedObject: 0x7368570> (entity: Cave; id: 0x7360110 <x-coredata://C825FC9D-3490-4D8A-A811-979B819A2EB6/Cave/p105> ; data: <fault>)",
    "<NSManagedObject: 0x7368610> (entity: Cave; id: 0x73303c0 <x-coredata://C825FC9D-3490-4D8A-A811-979B819A2EB6/Cave/p112> ; data: <fault>)"
)

它曾经完美地工作,直到我在Cave.m进行了以下更改,这是实体

我在Cave.h中添加了MKAnnotation作为委托,并在Cave.m中添加了此代码

- (CLLocationCoordinate2D)coordinate
{
    CLLocationCoordinate2D location;
    location.latitude = [self.latitude doubleValue];
    location.longitude = [self.longitude doubleValue];
    return location;
}

有没有办法调试这个？

Answer 1

这是预期的行为,在您需要访问对象的持久值之前,核心数据不会返回完整对象.在此之前,每个返回的对象都将是"错误".

您可以强制获取请求以使用返回完整对象[request setReturnsObjectsAsFaults:NO],但在大多数情况下,您可以使用它.有关更多信息,请查看NSFetchRequest的文档.

如果您访问其中一个属性,核心数据将转到持久性存储并获取其余值,然后您将在日志中获得完整描述.

这似乎是一种常见的误解,我决定在这里写下来.

Answer 2

我在从 CoreData 中提取数据时遇到了同样的问题！所以，我按照@jrturton 指示的方式在Swift 3 中实现了它：

第 1 步：添加 import CoreData

第 2 步：添加下面的代码。.

let context = ( UIApplication.shared.delegate as! AppDelegate ).persistentContainer.viewContext
var request = NSFetchRequest<NSFetchRequestResult>()
request = Your_Entity_Name.fetchRequest()
request.returnsObjectsAsFaults = false
do {
    let arrayOfData = try context.fetch(request)
} catch {
    // Handle the error! 
}

希望，它会帮助你。:)