Swift coreData - format date and use it in predicate

问题

H. I have an entity called Agendadate and one called AgendaEvent. AgendaEvent has a many to many relation with AgendaDate (agendaDates).

in my AgendaDate i have an object dates (of type Date).

I'm using a predicate like so:

fetchRequest.predicate = NSPredicate(format: "ANY agendaDates.dates == %@", date as CVarArg)

I'm trying to format dates to have this:

"dd MM yyyy" instead of "yyyy MM dd hh:mm:ss"

I need to compare in the predicate two dates but without the time? is it possible?

UPDATE----- Here's my function updated as you have suggested:

func agendaEventsWithDate(date: Date) -> NSFetchRequest<AgendaEvent>
{
    // create a fetch request that will retrieve all the AgendaEvents.
    let fetchRequest = NSFetchRequest<AgendaEvent>(entityName: "AgendaEvent")

    // set the predicate to only keep AgendaEvents where the related AgendaDate's date matches the passed in date.
    let cal = Calendar.current
    let startOfDay = cal.startOfDay(for: eventDate)
    let endOfDay = cal.date(byAdding: .day, value: 1, to: startOfDay)!
    print(startOfDay)
    print(endOfDay)
    // fetchRequest.predicate = NSPredicate(format: "ANY agendaDates.agendaDates == %@", date as CVarArg)
     fetchRequest.predicate = NSPredicate(format: "SUBQUERY(agendaDates, $a, $a.dates >= %@ AND $a.dates < %@).@count > 0",
                                startOfDay as NSDate, endOfDay as NSDate)

    return fetchRequest
}

and here's the function that should configure the cell and take just the events which have the same date of the selected date:

func configuringCell(cell: CalendarAgendaCell, indexPath: IndexPath) {
    for dates in calendar.selectedDates {
        for dateOfEvent in myEventDate {
            formatter.dateFormat = "dd MM yyyy"
            let dateToCompare = formatter.string(from: dates)
            formatter.dateFormat = "dd-MM-yyyy"
            let comparingDate = formatter.date(from: dateToCompare)!
            if dateOfEvent == dateToCompare {
                myTempEvents = try! context.fetch(agendaEventsWithDate(date: comparingDate))
                let myEvent = myTempEvents[indexPath.row]
                cell.configureCell(agendaEvent: myEvent)

            } else {
               // the array is empty

            }
        }
    }
}

回答1:

Don't use a custom string format for that purpose. You want to fetch all entries which are related to an Agendadate object with a date on the same day as the given day.

So you compute the start and end of that day first:

let date = Date()

let cal = Calendar.current
let startOfDay = cal.startOfDay(for: date)
let endOfDay = cal.date(byAdding: .day, value: 1, to: startOfDay)!

Then use this SUBQUERY:

let predicate = NSPredicate(format: "SUBQUERY(agendaDates, $a, $a.dates >= %@ AND $a.dates < %@).@count > 0",
                            startOfDay as NSDate, endOfDay as NSDate)

It tests $a.dates >= startDate AND $a.dates < endDate for all related objects, and yields true if there is at least one matching the condition.

来源：https://stackoverflow.com/questions/46217293/swift-coredata-format-date-and-use-it-in-predicate

标签

ios

swift

core-data

nspredicate