Question

I’m trying to filter an array of objects selecting those where a property of type NSDate are equal to a specific date. However, I only want to compare the date and ignore any time difference.

So I’m using an NSPredicate as so:

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"PropertyWithDate == %@", 
                      [NSDate date]];

As both the object is storing the date with time and the value for now I am passing holds both. How do I arrange it to ignore the time part in both during the comparison?

Answer 1

Remember, an NSDate expresses a point in time, independent of timezones, so it only makes sense to talk about the date part of an NSDate with respect to a specific calendar and timezone.

The short answer is that you’ll need to construct two NSDates: one for 12am the day of your date, and one for 12am the day after, and then set up your predicate to look for dates between the two:

NSPredicate *firstPredicate = [NSPredicate predicateWithFormat:@"PropertyWithDate > %@", firstDate];
NSPredicate *secondPredicate = [NSPredicate predicateWithFormat:@"PropertyWithDate < %@", secondDate];

NSPredicate *predicate = [NSCompoundPredicate andPredicateWithSubPredicates:[NSArray arrayWithObjects:firstPredicate, secondPredicate, nil]];

To construct firstDate and secondDate, you’ll want to use NSCalendar‘s components:fromDate: and dateFromComponents: methods. If you want to use the device’s current default calendar and timezone, you can just use [NSCalendar calendar] to get a calendar to use.