核心数据，无法保存上下文

Question

I'm simply trying to save a ManagedObjectContext but while I get no errors, the fetched request returns the object with none of the saved values. Consider this simple example. You have a single object, you change a property and save it. The object is there but the property is not saved. As you can see, I want only one object, and the fetch returns this one object. BTW, the code is in a simple class, not the app delegate or a view controller.

Here is the sample code:

MyAppDelegate* delegate = [[UIApplication sharedApplication] delegate];

NSManagedObjectContext* context = delegate.managedObjectContext;

NSEntityDescription *myEntityDesc = [NSEntityDescription entityForName:@"MyEntity" inManagedObjectContext:context];

NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease];

[request setEntity:myEntityDesc];

NSError *error = nil;

NSArray *array = [context executeFetchRequest:request error:&error];
MyEntity* myEntity;

if (array == nil || [array count] < 1)
{
    myEntity = [NSEntityDescription insertNewObjectForEntityForName:@"MyEntity" inManagedObjectContext:context];
}
else 
{
    myEntity = [array objectAtIndex:0];
}

myEntity.BoolValue = [NSNumber numberWithBool:someBoolValue];
myEntity.ID = @"Some ID";

if ([context save:&error])
{
    NSLog(@"no error");
}
else 
{
    NSLog([NSString stringWithFormat:@"found core data error: %@", [error localizedDescription]]);
}

Here's the code used to retrieve the values later:

MyAppDelegate* delegate = [[UIApplication sharedApplication] delegate];

NSManagedObjectContext* context = delegate.managedObjectContext;

NSEntityDescription *MyEntityDesc = [NSEntityDescription entityForName:@"MyEntity" inManagedObjectContext:context];

NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease];

[request setEntity:MyEntityDesc];

NSError *error = nil;

NSArray *array = [context executeFetchRequest:request error:&error];

MyEntity* myEntity;

if (array == nil || [array count] < 1)
{
    //handle error
}
else 
{
    myEntity = [array objectAtIndex:0];
}

return [myEntity.BoolValue boolValue];

Answer 1

What does your NSManagedObject subclass look like? Since the fetch is working correctly (ie returning the entity), I suspect something is wrong in the subclass implementation.

You should declare a @property for each of the attributes on your data model. And in the implementation file, instead of using @synthesize you need to use @dynamic . Also make sure in your xcdatamodel that the entity has its class set, as well as the name.

@interface MyEntity : NSManagedObject
@property (nonatomic, strong) NSNumber * boolValue;

@end

@implementation MyEntity
@dynamic boolValue;

@end