Swift 4.1 JSON to Struct then to array of distinct dates - json

Question

I am calling an API that returns a JSON result of appointments. Example:
[{"DiarySummary":"Test appointment","DiaryDescription":"Test","DiaryId":"62","EventNo":"","EventTypeId":"","StartDateTime":"07/06/2018 09:00:51","StopDateTime":"07/06/2018 21:00:51","DayHalfDay":"0","AgentGroupName":"DEV","AgentInitials":"AC","AgentId":"5","OwnerShortName":"","OwnerLongName":"","AbsenceTypeDescription":"Working From Home","AbsenceTypeId":"15"}...
I have this mapping to a struct in my code using the decode function:
struct DiaryAppointment: Decodable {
let DiarySummary: String?
let DiaryDescription: String?
let DiaryId: String?
let EventNo: String?
let EventTypeId: String?
let StartDateTime: String?
let StopDateTime: String?
let DayHalfDay: String?
let AgentGroupName: String?
let AgentInitials: String?
let AgentId: String?
let OwnerShortName: String?
let OwnerLongName: String?
let AbsenceTypeDescription: String?
let AbsenceTypeId: String?
}
self.appointments = try JSONDecoder().decode([DiaryAppointment].self, from: data!)
and then the self.appointments array is being used in a UICollectionView. All of this works absolutely fine. However, I would like to split the collectionView into sections based on distinct StartDates with a header fro each.
I have tried creating a secondary array, but the value of StartDateTime in my JSON and therefore in my appointments array is a string as opposed to a date. I can loop through the appointments array and convert the value of appointment.StartDateTime to a date object and add to a new array which should allow me to pick out distinct dates, but I won't be able to split the original appointments array because the value is still a string.
Is it possible convert this to a date object at the point off calling decode? If not, how can I achieve the required functionality, or, is there a better way to do this?

Answer 1

First of all use CodingKeys to get lowercased variable names and declare the properties as much non-optional as possible:
struct DiaryAppointment: Decodable {
private enum CodingKeys: String, CodingKey {
case diarySummary = "DiarySummary", diaryDescription = "DiaryDescription", diaryId = "DiaryId"
case eventNo = "EventNo", eventTypeId = "EventTypeId", startDateTime = "StartDateTime"
case stopDateTime = "StopDateTime", dayHalfDay = "DayHalfDay", agentGroupName = "AgentGroupName"
case agentInitials = "AgentInitials", agentId = "AgentId", ownerShortName = "OwnerShortName"
case ownerLongName = "OwnerLongName", absenceTypeDescription = "AbsenceTypeDescription", absenceTypeId = "AbsenceTypeId"
}
let diarySummary, diaryDescription, diaryId, eventNo, eventTypeId: String
let startDateTime, stopDateTime: Date
let dayHalfDay, agentGroupName, agentInitials, agentId: String
let ownerShortName, ownerLongName, absenceTypeDescription, absenceTypeId: String
}
Declare startDateTime and stopDateTime as Date and pass a DateFormatter as dateDecodingStrategy
let decoder = JSONDecoder()
let dateFormatter = DateFormatter()
dateFormatter.locale = Locale(identifier: "en_US_POSIX")
dateFormatter.dateFormat = "dd/MM/yyyy HH:mm:ss"
decoder.dateDecodingStrategy = .formatted(dateFormatter)