How to deal with [NSDate] and Firebase

Question

I am making a calendar app. I have one array of selected dates. User selected it previously and they are stored there.

var selectedDays = [NSDate]()

When app loads I have to display these dates, but everything is overcomplicated because Firebase doesn't accept NSDate

I have another array var selectedDaysForFirebase = [String]() which is the same array as above only dates are converted to strings to accomodate Firebase.

This is how I save selected dates:

// 1. Append converted date into selectedDaysForFirebase array
            let day = dateFormatter.stringFromDate(date)
            selectedDaysForFirebase.append(day)

// 2. Push data to Firebase
            ref.childByAppendingPath("dates").setValue(selectedDaysForFirebase)

My Firebase has user auth. so every user has it's own little database with dates.

In my viewDidLoad I have to grab that dates array from Firebase and store it in my selectedDates array which accepts NSDate

ref.childByAppendingPath("dates").observeEventType(.Value, withBlock: { snapshot in

        if let dates = snapshot.value as? NSArray {
             print(dates)
             // convert firebase array of dates with array of dates that only accepts NSDate
        }

        }, withCancelBlock: { error in
             print(error.description)
        })

This outputs:

(
    "2016-04-10",
    "2016-04-11",
    "2016-04-12"
)

I think there is a better way to store dates and then retreive it and I hope somebody could help me with this.

Answer 1

The answer really depends on how you are using your date.

'numbers' cannot be stored in Firebase; any numeric value is first converted (by Firebase) to NSNumber for storage. See Understanding Data

You need to determine how you will be using your date and how much granularity will be needed. In some cases

2016-04-06

is enough, but other times you may need more

2016-04-06 14:00:00

I would suggest simply storing these as strings as they are sortable, easily manipulated and can be brought into a NSDate object or taken out of an NSDate object.

Here's some sample code to convert NSDate to a formatted string, similar to a time stamp, which can then be stored in Firebase as a string.

NSDateFormatter *dateFormat = [NSDateFormatter new];
[dateFormat setDateFormat: @"yyyy-MM-dd HH:mm:ss zzz"];

NSString *dateString = [dateFormat stringFromDate:[NSDate date]];

NSLog(@"%@",dateString);

and the other way from formatted string to NSDate

NSDate *d = [NSDate new];

d = [dateFormat dateFromString:dateString];

NSLog(@"the date %@", d);

The super most important thing is: keep it consistent. However you do it, do it the same way every time in your code.

Oh - one other thing. Array's. Array's should be used sparingly and only in specific use case situations in Firebase. They can be challenging to work with as you don't have access to specific indexes or have the ability to change, add or remove a single index.

Here's a much better structure

my_dates
    date_0
      date_stamp: 2016-04-06
    date_1
      date_stamp: 2016-04-07

the date keys (date_0, date_1) are generated with childByAutoId.

Answer 2

get a date from a double:

var interval = Double()
var date = NSDate()
date = NSDate(timeIntervalSince1970: interval)

other way around, get double from date:

interval = date.timeIntervalSince1970