Why is an NSDate in a Core Data managed Object converted to NSTimeInterval?

Question

I have an object with a property with a Date type defined in my xcdatamodeld object. Why has it generated the NSManagedObject class with a NSTimeInterval? And how do I set a

Answer 1

If you want to have mixed entities that uses both scalar and non-scalar property representations such as int32_t for integer or boolean properties but NSDate* for date properties, you need to manually edit the generated managed object .h file.

Therefore I usually start with creating managed object classes by checking the option Use scalar properties for primitive data types (as I have more integer and boolean properties than dates). Then I edit the created header file as follows:

MYEntity.h

@interface MYEntity : NSManagedObject
@property (nonatomic) int32_t index;
@property (nonatomic) NSTimeInterval date;
@end

then becomes:

@interface MYEntity : NSManagedObject
@property (nonatomic) int32_t index;
@property (nonatomic, retain) NSDate * date;
@end

If you are of the kind who doesn't like to manually edit this file, you can also choose to add a convenience property using a category that allows for accessing the scalar property as if it would be an object.

MYEntity+Convenience.h:

@interface MYEntity (Convenience)
@property (nonatomic, readwrite) NSDate *theDate
@end

MYEntity+Convenience.h:

@implementation MYEntity (Convenience)

- (NSDate *)theDate {
    return [NSDate dateWithTimeIntervalSinceReferenceDate:self.date];
}

- (void)setTheDate:(NSDate *)theDate {
    self.date = [theDate timeIntervalSinceReferenceDate]
}

@end

To make the code more readable in this example I would name the original property dateTimeInterval in the data model designer and the convenience property with its desired name: date.

The second approach obviously also works vice versa. You can export your entities with non-scalar properties and then provide a convenience scalar property whose getter and setter accesses the original non-scalar property.