Adding an Object to Cloud Firestore using Flutter

Null safe code:

Say this is your object.

class MyObject {
  final String foo;
  final int bar;

  MyObject._({required this.foo, required this.bar});

  factory MyObject.fromJson(Map<String, dynamic> data) {
    return MyObject._(
      foo: data['foo'] as String,
      bar: data['bar'] as int,
    );
  }

  Map<String, dynamic> toMap() {
    return {
      'foo': foo,
      'bar': bar,
    };
  }
}

To add this object to the cloud firestore, do:

MyObject myObject = MyObject.fromJson({'foo' : 'hi', bar: 0}); // Instance of MyObject.

var collection = FirebaseFirestore.instance.collection('collection');
collection
    .add(myObject.toMap()) // <-- Convert myObject to Map<String, dynamic>
    .then((_) => print('Added'))
    .catchError((error) => print('Add failed: $error'));

first, i highly recommend you have a single file that defines all of your schemas and/or models so there's a single point of reference for your db structure. like some file named dbSchema.dart:

import 'package:meta/meta.dart';

class Replies {

  final String title;  
  final Map coordinates;

  Replies({
    @required this.title,
    @required this.coordinates,
  });

 Map<String, dynamic> toJson() =>
  {
    'title': title,
    'coordinates': coordinates,
  };

}

and make the field that you want to be an object type Map. then, on the page you're going to insert into the db, import dbSchema.dart and create a new model:

Replies _replyObj = new Replies(
  title: _topic,
  coordinates: _coordinates,
);

this assumes you've defined your local _coordinates (or whatever) object prior to this, with something like :

_coordinates = {
 'lat': '40.0000',
 'lng': '110.000', 
};

and to then insert into Firestore, add the object's toJson method (you cannot insert/update a plain Dart model):

CollectionReference dbReplies = Firestore.instance.collection('replies');

Firestore.instance.runTransaction((Transaction tx) async {
  var _result = await dbReplies.add(_replyObj.toJson());
  ....

Update (5/31)

To convert the document read back into an object you need to add a fromJson to the class, like so:

Replies.fromJson(Map parsedJson) {
    id = parsedJson['id']; // the doc ID, helpful to have
    title = parsedJson['title'] ?? '';
    coordinates = parsedJson['coordinates'] ?? {};
}

so when you query the db:

QuerySnapshot _repliesQuery = await someCollection
        .where('title', isEqualTo: _title)
        .getDocuments();

List<DocumentSnapshot> _replyDocs = _repliesQuery.documents;

you can create an object out of each snapshot:

for (int _i = 0; _i < _replyDocs.length; _i++) {

  Replies _reply = Replies.fromJson(_replyDocs[_i].data);
  _reply.id = _replyDocs[_i].documentID;

  // do something with the new _reply object
}

@Laksh22 As far as I understand, you mean something like this:

Firestore.instance.runTransaction((transaction) async {
    await transaction.set(Firestore.instance.collection("your_collection").document(), {
        'reply' : {
        'replyName': replyName,
        'replyText': replyText,
        'replyVotes': replyVotes,
    }
});

just like the screenshot above.

You can run a Firestore transaction like this:

    Firestore.instance.runTransaction((transaction) async {
          await transaction.set(Firestore.instance.collection("your_collection").document(), {
            'replyName': replyName,
            'replyText': replyText,
            'replyVotes': replyVotes,
          });
        });