是否可以在Firestore时间戳/日期中使用“可解码”？

Question

I have a dictionary that's a [String: Bookmark] but that createdAt is saved as a Timestamp and the decoder throws an error when trying to make sense of the Date

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Invalid type in JSON write (__NSDate)'

struct Bookmark: Decodable {
    let messageId: String
    let messageCreatedAt: Date
}


JSONDecoder().decode([String: Bookmark].self, data: data)

Is there a way yet to make Swift's Decodable protocol play nicely with Firestore Timestamps?

Edit:

If I print the [String: Any] and then try to decode in the console like so

 ▿ 1 : 2 elements
    - key : "messageCreatedAt"
    - value : 2018-11-27 20:59:11 +0000

po valueDict["messageCreatedAt"] as? Date

I get

▿ Optional<Date>
  ▿ some : 2018-11-27 20:59:11 +0000
    - timeIntervalSinceReferenceDate : 565045151.531769

So it must be something in Decodable then that isn't able to identify and parse this?

Edit:

JSON is

{
  "messageId": "abc123",
  "messageCreatedAt": "2018-11-27 20:59:11 +0000"
}

Answer 1

How is JSONDecoder is decoding dates is defined by value of .dateDecodingStrategy property.

If you have to parse Date from a string you should use either .iso8601 or .formatted(_:) (or if your date format is really custom and complicated and/or weird you may to have use .custom(_:) ).

Your date string is almost ISO 8601 formatted (it only lacks T between date and time parts), but that's enough to fail.

So your best option here is to use formatted(_:) :

// Declare it somewhere and reuse single instance as much as possible, formatter initialization is quite expensive
let dateFormatter = DateFormatter()
dateFormatter.locale = Locale(identifier: "en_US_POSIX") // Better to fix Locale here
dateFormatter.dateFormat = "yyyy-MM-dd kk:mm:ss Z"

And then

let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .formatted(dateFormatter)
let bookmark = try decoder.decode(Bookmark.self, from: data) 

print(bookmark.messageCreatedAt, bookmark.messageCreatedAt.timeIntervalSince1970)
// prints "2018-11-27 20:59:11 +0000 1543352351.0"