Easiest Way to overcome operator assignment in dart - flutter

Question

I am developing a flutter app.My flutter project shows error in factory constructor when I use DocumentSnapshot
User.dart
import 'package:cloud_firestore/cloud_firestore.dart';
class User {
final String id;
final String username;
final String email;
final String photoUrl;
final String displayname;
final String bio;
User({
this.id,
this.username,
this.email,
this.photoUrl,
this.displayname,
this.bio
});
factory User.fromDoc(DocumentSnapshot doc){
return User(
id: doc['id'],
username: doc['username'],
email: doc['email'],
photoUrl: doc['photoUrl'],
displayname: doc['displayName'],
bio: doc['bio'],
);
}
}
Error log
Launching lib\main.dart on sdk gphone x86 arm in debug mode...
Running Gradle task 'assembleDebug'...
lib/models/user.dart:22:14: Error: The operator '[]' isn't defined for the class 'DocumentSnapshot'.
- 'DocumentSnapshot' is from 'package:cloud_firestore/cloud_firestore.dart' ('/C:/flutter/flutter/.pub-cache/hosted/pub.dartlang.org/cloud_firestore-0.14.0+2/lib/cloud_firestore.dart').
Try correcting the operator to an existing operator, or defining a '[]' operator.
id: doc['id'],
^
lib/models/user.dart:23:20: Error: The operator '[]' isn't defined for the class 'DocumentSnapshot'.
- 'DocumentSnapshot' is from 'package:cloud_firestore/cloud_firestore.dart' ('/C:/flutter/flutter/.pub-cache/hosted/pub.dartlang.org/cloud_firestore-0.14.0+2/lib/cloud_firestore.dart').
Try correcting the operator to an existing operator, or defining a '[]' operator.
username: doc['username'],
^
lib/models/user.dart:24:17: Error: The operator '[]' isn't defined for the class 'DocumentSnapshot'.
- 'DocumentSnapshot' is from 'package:cloud_firestore/cloud_firestore.dart' ('/C:/flutter/flutter/.pub-cache/hosted/pub.dartlang.org/cloud_firestore-0.14.0+2/lib/cloud_firestore.dart').
Try correcting the operator to an existing operator, or defining a '[]' operator.
email: doc['email'],
^
lib/models/user.dart:25:20: Error: The operator '[]' isn't defined for the class 'DocumentSnapshot'.
- 'DocumentSnapshot' is from 'package:cloud_firestore/cloud_firestore.dart' ('/C:/flutter/flutter/.pub-cache/hosted/pub.dartlang.org/cloud_firestore-0.14.0+2/lib/cloud_firestore.dart').
Try correcting the operator to an existing operator, or defining a '[]' operator.
photoUrl: doc['photoUrl'],
^
lib/models/user.dart:26:23: Error: The operator '[]' isn't defined for the class 'DocumentSnapshot'.
- 'DocumentSnapshot' is from 'package:cloud_firestore/cloud_firestore.dart' ('/C:/flutter/flutter/.pub-cache/hosted/pub.dartlang.org/cloud_firestore-0.14.0+2/lib/cloud_firestore.dart').
Try correcting the operator to an existing operator, or defining a '[]' operator.
displayname: doc['displayName'],
^
lib/models/user.dart:27:15: Error: The operator '[]' isn't defined for the class 'DocumentSnapshot'.
- 'DocumentSnapshot' is from 'package:cloud_firestore/cloud_firestore.dart' ('/C:/flutter/flutter/.pub-cache/hosted/pub.dartlang.org/cloud_firestore-0.14.0+2/lib/cloud_firestore.dart').
Try correcting the operator to an existing operator, or defining a '[]' operator.
bio: doc['bio'],
^
FAILURE: Build failed with an exception.
* Where:
Script 'C:\flutter\flutter\packages\flutter_tools\gradle\flutter.gradle' line: 896
* What went wrong:
Execution failed for task ':app:compileFlutterBuildDebug'.
> Process 'command 'C:\flutter\flutter\bin\flutter.bat'' finished with non-zero exit value 1
* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.
* Get more help at https://help.gradle.org
BUILD FAILED in 7s
Exception: Gradle task assembleDebug failed with exit code 1
Is there any way to correct this operator problem because I have to use DocumentSnapshot in various sections of my app? If there any permanent solution available to use this kind of methods?
Thank You

Answer 1

If you want to access the firebases DocumentSnapshot you need to access its data attribute snapshot.data. If you want to access the map behind it use snapshot.data.data
So in your example something like:
factory User.fromDoc(DocumentSnapshot doc){
return User(
id: doc.data.data['id'],
username: doc.data.data['username'],
email: doc.data.data['email'],
photoUrl: doc.data.data['photoUrl'],
displayname: doc.data.data['displayName'],
bio: doc.data.data['bio'],
);
}
}
See the One-Time Read section in the official documentation:
https://firebase.flutter.dev/docs/firestore/usage/