How to retrieve Timestamp from Firebase?

Question

I have the starts and ends fields in my model as Timestamp, but I am getting this error. I don't get it when I define start and end as var in my Model.

Unhandled Exception: type 'Null' is not a subtype of type 'Timestamp'

Model:

    import 'package:cloud_firestore/cloud_firestore.dart';

class Event {
  String eid;
  String title;
  String location;
  Timestamp start;
  Timestamp end;
  String instructor;
  String image;
  String description;

  Event({
    required this.eid,
    required this.title,
    required this.location,
    required this.start,
    required this.end,
    required this.instructor,
    required this.image,
    required this.description
  });

  factory Event.fromMap(Map<String, dynamic>? map) {
    return Event(
      eid: map?['eid'] ?? 'undefined',
      title: map?['title'] ?? 'undefined',
      location: map?['location'] ?? 'undefined',
      start: map?['starts'],
      end: map?['ends'],
      instructor: map?['instructor'] ?? 'undefined',
      image: map?['image'] ?? 'undefined',
      description: map?['description'] ?? 'undefined'
    );
  }

Answer 1

You are getting null value for start and end , you need to define a default value for them like other variable:

factory Event.fromMap(Map<String, dynamic>? map) {
    return Event(
      eid: map?['eid'] ?? 'undefined',
      title: map?['title'] ?? 'undefined',
      location: map?['location'] ?? 'undefined',
      start: map?['starts'] ?? Timestamp(0, 0),//<--- add this
      end: map?['ends'] ?? Timestamp(0, 0),//<--- add this
      instructor: map?['instructor'] ?? 'undefined',
      image: map?['image'] ?? 'undefined',
      description: map?['description'] ?? 'undefined'
    );
  }

Answer 2

start: map?['starts'],
end: map?['ends'],

What you are doing here is setting the start/end arguments to the map from firestore, but if the document doesn't have that field, you have no fallback and it returns null .

Do one of either:

1. Add a fallback value to the arguments, eg the current timestamp or some other:

start: map?['starts'] ?? Timestamp.now(),
end: map?['ends'] ?? Timestamp.now(),

2. Make the Timestamp nullable, if you expect things might be null there:

class Event {
  // ...
  Timestamp? start;
  Timestamp? end;

Answer 3

This is because you are not giving a default value (the same way you are doing for all other variables):

?? 'undefined'

One possible solution is to allow for null values... just add ? for both variables definitions, like this:

class Event {
  String eid;
  String title;
  String location;
  Timestamp? start; // *** change 1
  Timestamp? end;   // *** change 2
  String instructor;
  String image;
  String description;

Let me know if this does not work.