iPhone CoreData：如何按天分组获取的结果？

I am developing an iPhone App with CoreData. One of my entities has an NSDate property named 'time'. It stores times to the minute/second. As my sections i'd like to have the date to the day. So if there are to entries '2010-06-14 8:00' and '2010-06-14 11:00', i'd like them to be grouped to '2010-06-14'.I am developing an iPhone App with CoreData. On