How to store data into model using fromJson in flutter firebase? - firebase

Question

Currently I'm working on a flutter project. I'm trying to create a function that gets snapshot from Firebase document and stores it into userData model using fromJson function.
Here's my User.dart
class UserData {
// final String uid;
final String usn;
final String fullName;
final int? sem;
final String branch;
final String section;
UserData({
required this.usn,
required this.fullName,
required this.sem,
required this.branch,
required this.section,
});
factory UserData.fromJson(Map<String, dynamic> json) {
return UserData(
usn: json['usn'],
fullName: json['fullName'],
sem: json['sem'],
branch: json['branch'],
section: json['section']);
}
Map<String, dynamic> toMap() {
return {
'usn': usn,
'fullName': fullName,
'sem': sem,
'branch': branch,
'section': section
};
}
}
In my database.dart
I want to create a Stream function in it to map to fromJson
Here's what I have tried
Stream<UserData?> curUserData() {
return _db.collection('users').doc(user.uid).snapshots()
.map((DocumentSnapshot snapshot) => UserData.fromJson(snapshot.data()));
}
Can anyone rectify the function?
I am getting error from above function.

Answer 1

Your problem is just wrong type assertion. Try this:
Change DocumentSnapshot for DocumentSnapshot<Map<String, dynamic>>
Stream<UserData?> curUserData() {
return _db.collection('users').doc(user.uid).snapshots()
.map((DocumentSnapshot<Map<String, dynamic>> snapshot) => UserData.fromDocument(snapshot.data()!));
}

Answer 2

This example is for my case with cloud_firestore: ^3.1.7:
getLastStageNumber() async {
QuerySnapshot querySnapshot = await stagesRef
.orderBy('stage_number', descending: true)
.limit(1)
.get();
StageMod stageMod;
if (querySnapshot.docs.isNotEmpty) {
stageMod = StageMod.fromJson(
querySnapshot.docs.first.data()! as Map<String, dynamic>);
lastStageNumber = stageMod.stageNumber;
}
}