Core Data Predicate Filter By Today's Date

Question

I had issues with this and I haven't found a proper answer on SO so I'll leave a small tutorial here.

The goal is to filter fetched objects by today's date.

Note: It's Swift 3 compatible.

Answer 1

You can't simply use to compare your date to today's date:

let today = Date()
let datePredicate = NSPredicate(format: "%K == %@", #keyPath(ModelType.date), today)

It will show you nothing since it's unlikely that your date is the EXACT comparison date (it includes seconds & milliseconds too)

The solution is this:

// Get the current calendar with local time zone
var calendar = Calendar.current
calendar.timeZone = NSTimeZone.local

// Get today's beginning & end
let dateFrom = calendar.startOfDay(for: Date()) // eg. 2016-10-10 00:00:00
let dateTo = calendar.date(byAdding: .day, value: 1, to: dateFrom)
// Note: Times are printed in UTC. Depending on where you live it won't print 00:00:00 but it will work with UTC times which can be converted to local time

// Set predicate as date being today's date
let fromPredicate = NSPredicate(format: "%@ >= %@", date as NSDate, dateFrom as NSDate)
let toPredicate = NSPredicate(format: "%@ < %@", date as NSDate, dateTo as NSDate)
let datePredicate = NSCompoundPredicate(andPredicateWithSubpredicates: [fromPredicate, toPredicate])
fetchRequest.predicate = datePredicate

It's by far the easiest & shortest way of showing only objects which have today's date.

Answer 2

In swift4, Lawrence413's can be simplify a bit:

//Get today's beginning & end
let dateFrom = calendar.startOfDay(for: Date()) // eg. 2016-10-10 00:00:00
let dateTo = calendar.date(byAdding: .day, value: 1, to: dateFrom)

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It get rid of the component part, makes the code have better readability.