iOS Realm grouping by date to tableView sections - ios

Question

I have realm database, which contains data and date of adding this data. I want to exctract this and set date as table view section header and data as rows data for each section depend on date. I know how to exctract but dont know how to group by date and set data for each section depend on date. Thank you!

Answer 1

Swift 4 implementation using higher order functions rather then loops.
class Item: Object {
#objc dynamic var id: Int = 0
#objc dynamic var date: Date = Date()
}
let realm = try! Realm()
// fetch all Items sorted by date
let results = realm.objects(Item.self).sorted(byKeyPath: "date", ascending: false)
let sections = results
.map { item in
// get start of a day
return Calendar.current.startOfDay(for: item.date)
}
.reduce([]) { dates, date in
// unique sorted array of dates
return dates.last == date ? dates : dates + [date]
}
.compactMap { startDate -> (date: Date, items: Results<Item>) in
// create the end of current day
let endDate = Calendar.current.date(byAdding: .day, value: 1, to: startDate)!
// filter sorted results by a predicate matching current day
let items = results.filter("(date >= %#) AND (date < %#)", startDate, endDate)
// return a section only if current day is non-empty
return items.isEmpty ? nil : (date: startDate, items: items)
}

Answer 2

You can just sort your retrieved Results by date and then split them up while iterate through to make them accessible in a grouped / hierarchic manner.
class Person {
dynamic var name = ""
dynamic var date = NSDate()
}
let sortedObjects = realm.objects(Person).sorted("date")
var lastDate = objects.first?.date
let calendar = NSCalendar.currentCalendar()
var lastGroup = [Person]()
var groups = [[Person]]()
for element in sortedObjects {
let currentDate = element.date
let difference = calendar.components([.Year, .Month, .Day], fromDate: lastDate!, toDate: currentDate, options: [])
if difference.year > 0 || difference.month > 0 || difference.day > 0 {
lastDate = currentDate
groups.append(lastGroup)
lastGroup = [element]
} else {
lastGroup.append(element)
}
}
groups.append(lastGroup)
Note: In that way, you would need to keep all your elements in memory. If that shouldn't work out for you, depending on your use-case, you could memorize only the indexes instead, which you can use to access the element from the retrieved Results.

Answer 3

I had the exact same issue, I needed to display one kind of Realm entities in a sectioned table, grouped by date, and this is how I did it.
Example class containing the date field:
final class Appointment: Object {
#objc dynamic var id: Int = 0
#objc dynamic var date: Date?
}
Example code that will get all objects and split them in sections/results, grouped by unique date:
// (un)safely get an instance of Realm
let realm = try! Realm()
// get all the dates
// note that begginingOfDay is a extension on Date
// which gives back the beggining of the day of the given Date as a Date
// we are doing this in order to filter out non-unique dates later
let dates = self.realm.objects(Appointment.self).toArray().flatMap({ $0.date ?? nil }).map({ $0.beginningOfDay() })
// cast it to a Set to make values unique, and back to an Array for further use
let uniqueDates = Array(Set(dates))
let predicates = uniqueDates.map({ date -> NSPredicate in
// in order to use Swift's Date with NSPredicate
// it must be casted to NSDate
let begginingOfDay = date.beginningOfDay() as NSDate
let endOfDay = date.endOfDay() as NSDate
// create a predicate that checks if the given Date is in between
// the beggining of a given Date and the end of the given Date
let predicate = NSPredicate(format: "(date >= %#) AND (date <= %#)", begginingOfDay, endOfDay)
return predicate
})
// create an array of Results<Appointment>, and then use it to drive your table/collection view
// I will leave this part to you, depends on your UI implementation
// personally, I wrap this into another object that contains results, section index, section title, etc.
// and then I use all of that in my table view's data source methods
let sectionedResults: [Results<Appointment>] = predicates.map({ predicate -> Results<Appointment> in
let results = realm.objects(Appointment.self).filter(predicate)
return results
})
You should now have a rough idea how to do it know, I'll leave the details of the UI implementation to you.

Answer 4

If someone is fighting with Swift 3.0 syntax:
var lastDate = dateObjects.first?.start
let calendar = Calendar.current
var lastGroup = [DateObject]()
var days = [[DateObject]]()
for dateObject in dateObjects {
let currentDate = dateObject.start
let unitFlags : Set<Calendar.Component> = [.era, .day, .month, .year, .timeZone]
let difference = calendar.dateComponents(unitFlags, from: lastDate!, to: currentDate)
if difference.year! > 0 || difference.month! > 0 || difference.day! > 0 {
lastDate = currentDate
days.append(lastGroup)
lastGroup = [travelTime]
} else {
lastGroup.append(dateObject)
}
}
days.append(lastGroup)