How does the iPhone SDK Core Data system store date types to sqlite?

Question

I used core data to do this:

NSManagedObjectContext *m = [self managedObjectContext];
Foo *f = (Foo *)[NSEntityDescription insertNewObjectForEntityForName:@"Foo" 
                                                        inManagedObjectContext:m];
f.created_at = [NSDate date];
[m insertObject:f];

NSError *error;
[m save:&error];

Where the created_at field is defined as type "Date" in the xcdatamodel.

When I export the sql from the sqlite database it created, created_at is defined as type "timestamp" and the values look like:

290902422.72624

Nine digits before the . and then some fraction.

What is this format? It's not epoch time and it's not julianday format.

Epoch would be:

1269280338.81213

julianday would be:

2455278.236746875 (notice only 7 digits before the . not 9 like I have)

How can I convert a number like 290902422.72624 to epoch time? Thanks!

Answer 1

Just add 978307200 to the number in core data and you'll get normal timestamp

NSString *coreDataTimestamp =@"464615485.832736"; //string of timestamp in coredata
NSTimeInterval timestamp = [coreDataTimestamp doubleValue] + 978307200;