How to structure data inside Core Data for the following scenario

Question

I have the a Person object store in Core Data which contains two attributes:

name
payment

Now I decided I want to also store the average of payments for a day/month/year.

How should I store this inside Core Data ? Inside the Person object ? Create new objects ?

Do not burden your core data stack. Your situation can be handled by creating logic in subClass (NSObject) or in view Controller(not preferred). Create a method that return float from payment attribute after making calculation on it. Use it when required. i.e. -(float) averageMonthlyPayment — Alok, Dec 13 '15 at 12:22

score 2 · Accepted Answer · edited May 23 '17 at 11:52

The solution is not to store summary data. You can add convenience methods to your managed object subclass to deliver the desired value. Something along these lines:

func averageForPeriod(startDate: NSDate, endDate: NSDate) -> Double {
    guard self.payments != nil else { return 0 }
    let periodPayments = (self.payments as Set<Payment>).filter {
         $0.date >= startDate && $0.date <= endDate
    }
    return periodPayments.valueForKeyPath("@avg.amount").doubleValue
}

NB: for comparing dates like this you need to define your own comparison function as shown here, or you can use NSTimeInterval.

How to structure data inside Core Data for the following scenario

1 Answers1