I am on my way with creating a habit tracking app which uses Core Data for storing the habits. Because I need to know when I completed a part of my habit, I created a different entity containing only a Date with a many to one relationship to the habit entity. So one habit has a reference to many different dates on which it was completed, and the other way around.

First question: Is this the best method for doing this? Because the longer someone uses the app the more cluttered it gets with dates.

Second question: If it is good, how do I count the times I completed some habit for one specific date or a specific time interval (eg. week). I currently just compactMap over an array and count the result, but when having around 150 items in this array, it gets rather slow:

withAnimation(.easeInOut) {
    let todayCount = habit.dateArray.compactMap { (Calendar.current.isDateInToday($0.date!)) }
    return todayCount.count
}

I currently add a Date like this:

let newhabit = HabitCompletionDate(context: viewContext)
newhabit.date = Date()
newhabit.item = habit

And delete like this:

let habitObject = habit.date?.allObjects.last
viewContext.delete(habitObject as! NSManagedObject)

I don´t need the specific time, only the day of completion would still be enough, but this was the only solution I could come up with.

I have seen someone saying that you could do something like this with an NSPredicate but I did not understand how. As you might have guessed by this rather basic questions, I have no real experience in Core Data and personally it often gives me headaches.

Thanks in advance!

I have seen someone saying that you could do something like this with an NSPredicate but I did not understand how.

You would do something like this:

let cal = Calendar.current

//testDate being the date you want to check for
let startDate = cal.startOfDay(for: testDate)
let endDate = cal.date(byAdding: .day, value: 1, to: startDate)

//assuming date is the name of your Core Data attribute
let predicate = NSPredicate(format: "date >= %@ AND date < %@", startDate, endDate)

Okay, that's a good starting point, thank you! How would I go about implementing it? I know I can use it in a fetch request so that would be useful for my List View, but what should I do when I already have my Habit-item, like I do in my DetailView?