Check Core Data for an entry with Today's Date & perform function - swift

Question

I am fairly new to Swift & hoping someone knows the answer to this - nothing I try seems to work!
I have a Swift app which has a Core Data entity called "Drink" with 2 keys: a Date & then one called "drinkWater" which stores a value of "1" when a button is pushed.
I am trying to write a separate function where I can check if an entry exists for todays date and, if so, perform an action (in this case change an imageview).
I realise the below isn't the answer but it's as far as I got! Basically I can get all of the entries based on the value of drinkWater (this would need to be by Date I am guessing?) and I can get today's date all printing to the console. Now I'm stuck ...
private func updateMyImageView() {
let appDelegate = UIApplication.shared.delegate as! AppDelegate
let context = appDelegate.persistentContainer.viewContext
let request = NSFetchRequest<NSFetchRequestResult>(entityName: "Drink")
request.predicate = NSPredicate(format: "drinkWater = %#", "1")
request.returnsObjectsAsFaults = false
do {
let result = try context.fetch(request)
for data in result as! [NSManagedObject] {
print(data.value(forKey: "timestamp") as! Date)
}
} catch {
print("Failed")
}
let dateNow = Date()
print("Date is \(dateNow)")
}
This returns:
2018-12-29 01:27:27 +0000
Date is 2018-12-29 12:21:21 +0000
Any ideas on how to turn this all into the correct function would be greatly appreciated!!

Answer 1

You need to use a date range from start of day to end of day (midnight to midnight) in a compound predicate. Here is a solution based on a similar SO question
var calendar = Calendar.current
calendar.timeZone = NSTimeZone.local
let dateFrom = calendar.startOfDay(for: Date())
let dateTo = calendar.date(byAdding: .day, value: 1, to: dateFrom)
let fromPredicate = NSPredicate(format: "timestamp >= %#", dateFrom as NSDate)
let toPredicate = NSPredicate(format: "timestamp < %#", dateTo! as NSDate)
let waterPredicate = NSPredicate(format: "drinkWater = %#", "1")
let request = NSFetchRequest<NSFetchRequestResult>(entityName: "Drink")
request.predicate = NSCompoundPredicate(andPredicateWithSubpredicates: [waterPredicate, fromPredicate, toPredicate])

Answer 2

Thank you for all of your help. I have it all working now. My final code is:
let appDelegate = UIApplication.shared.delegate as! AppDelegate
let context = appDelegate.persistentContainer.viewContext
var calendar = Calendar.current
calendar.timeZone = NSTimeZone.local
let dateFrom = calendar.startOfDay(for: Date())
let dateTo = calendar.date(byAdding: .day, value: 1, to: dateFrom)
let fromPredicate = NSPredicate(format: "timestamp >= %#", dateFrom as NSDate)
let toPredicate = NSPredicate(format: "timestamp < %#", dateTo! as NSDate)
let waterPredicate = NSPredicate(format: "drinkWater = %#", "1")
let request = NSFetchRequest<NSFetchRequestResult>(entityName: "Drink")
request.predicate = NSCompoundPredicate(andPredicateWithSubpredicates: [waterPredicate, fromPredicate, toPredicate])
do {
let result = try context.fetch(request)
for data in result as! [NSManagedObject] {
print(data.value(forKey: "timestamp") as! Date)
drinkMoreButton.setBackgroundImage(UIImage(named: "watericonselected.png"), for: UIControlState.normal)
}
} catch {
print("Failed")
}