So basically im taking a basic To Do app and adding functionality where users can check off items, but also get a calculated productivity for each day, and then display it in a graph. I have the graph set up with mock data. But my problem is how do I get all item s with equal dates so that I can perform the calculation:

( Number of tasks completed on the same day / Total number of tasks created on the same day )

My ItemEntity in Core Data has:

name : String date : Date isChecked: Bool productivity: Double

Ive been researching everything for the past few days. Things from using the BackgroundTask api to perform the calculation at 00:00 every day. Then I thought maybe use UserDefaults to store a reference date and when the user returns to the app, if the elapsed time >= 24 hours then the productivity will be set to 0%, otherwise perform the calculation and store the productivity. Now im thinking im over-complicating it and its as simple as finding a way to fetch items only with the same date and doing the calculation on them.

...help me

You will need to create a compound predicate using combined simple predicates that check the date (using predicate parameter substitution).

Try this approach from StackOverflow - CoreData fetch filtered on today.

If you want to "fetch" the same day then you should do it as above. However a better way is to retrive all then do a filter on the result as every time the date changes then will have re-query coredata.

Then you could add this extension

extension Date {
    func isDay(of date: Date) -> Bool {
        let calendar = Calendar.current
        guard let selfDate = calendar.date(from: calendar.dateComponents([.day, .month, .year], from: self)) else {
            fatalError("Unable to get start date from date")
        }

        guard let inputDate = calendar.date(from: calendar.dateComponents([.day, .month, .year], from: date)) else {
            fatalError("Unable to get start date from date")
        }
        return inputDate == selfDate
    }
}

And then if a user want a different data then it can look at that date Here a example

struct ContentView: View {
    @State private var date1 = Date.now
    @State private var date2 = Date.now

    var body: some View {
        VStack(spacing: 50) {
            DatePicker("Date1", selection: $date1, displayedComponents: .date)

            Image(systemName: date1.isDay(of: date2) ? "checkmark.circle" : "x.circle")
                .imageScale(.large)

            DatePicker("Date2", selection: $date2, displayedComponents: .date)
        }
        .padding()
    }
}

if you just want to check for today then do

Image(systemName: date1.isDay(of: Date.now) ? "checkmark.circle" : "x.circle")

Is there a reason to use this:

extension Date {
    func isDay(of date: Date) -> Bool {
        let calendar = Calendar.current
        guard let selfDate = calendar.date(from: calendar.dateComponents([.day, .month, .year], from: self)) else {
            fatalError("Unable to get start date from date")
        }

        guard let inputDate = calendar.date(from: calendar.dateComponents([.day, .month, .year], from: date)) else {
            fatalError("Unable to get start date from date")
        }
        return inputDate == selfDate
    }
}

over this:

extension Date {
    func isDay(of date: Date) -> Bool {
        Calendar.current.isDate(self, inSameDayAs: date)
    }
}

No. Did not know about isDate( ) that all. i just built it from a project to get the first day od month. Always learning something new. PS. is there something like .isToday() as well?

Yep, Calendar has several similar methods:

func isDateInToday(_ date: Date) -> Bool
func isDateInYesterday(_ date: Date) -> Bool
func isDateInTomorrow(_ date: Date) -> Bool