iOS Realm grouping by date to tableView sections

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.