How can I get the last uploaded data to Firebase?-CodePudding

StreamBuilder<QuerySnapshot<Map<String, dynamic>>>(
        stream: FirebaseFirestore.instance
            .collection('users')
            .where('bmi')
            .limit(1)
            .snapshots(),
        },
      )),


class User {
  final double bmi;

  User(
      {required this.bmi});

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

  static User fromJson(Map<String, dynamic> json) => User(
      bmi: json['bmi']);
}

I want to pull the last added 'bmi' value to firebase. Do I need to use the OrderBy() method?

I tried adding the .last method to the end of the snapshot. But

"The argument type 'Future<QuerySnapshot<Map<String, dynamic>>>' can't be assigned to the parameter type 'Stream<QuerySnapshot<Map<String, dynamic>>>?'.",

Gives a fault.

CodePudding user response：

Firestore has no built in concept of a timestamp for each document of when it was created or updated that you can use as a condition in a query.

If you need this, you'll have to add a timestamp field to each document yourself. Once that exists, you can get the latest document with:

FirebaseFirestore.instance
    .collection('users')
    .orderBy('yourTimestampField', descending: true)
    .limit(1)
    .snapshots(),
},

Also see the Firebase documentation on ordering and limiting data