How to make only the user who saved the String can see Flutter/Firebase?

Question

This is a code that saves a String qr code that does not repeat in the database, but this way everyone can access this data.  I already got the user ID but I still can’t filter to just see the list.

void SalvarMensagem() async {

  String uid = UserModel.of(context).firebaseUser.uid;

  this._status = _status;
  _numeroSerie = _status.substring(48, 80);

  final QuerySnapshot result = await Future.value(Firestore.instance
      .collection("lockers")
      .where("numero_serie", isEqualTo: "$_numeroSerie")
      .limit(1)
      .getDocuments());

  final List<DocumentSnapshot> documents = result.documents;
  if (documents.length == 1) {
   // duplicado(context);
  } else {
    await Firestore.instance
        .collection("lockers")
        .document()
        .setData({"numero_serie": _numeroSerie, "userId": uid});
  }
}

in the firebase bank:

Answer 1

You can store in your Customers lockers the user code that entered the Qrcode and then when filtering its lokers you bring only those who have the respective code.

When connecting to firebase you can authenticate by email/password, as follows

class Conection {
  final FirebaseAuth _firebaseAuth = FirebaseAuth.instance;

  Future<String> signInWithEmailAndPassword(String email, String password) async {
    FirebaseUser user = await _firebaseAuth.signInWithEmailAndPassword(email: email, password: password);
    user.email;
    return user?.uid;
  }
}

The method signInWithEmailAndPassword will return the Document code created in your Firebase. Save this code to identify which user logged in.

When saving your new Qrcode, do it this way

await Firestore.instance
    .collection("lockers")
    .document()
    .setData({"numero_serie": _numeroSerie, "userid": codigoSalvoAposConexao}); // se não existe grava no banco

So when you are going to filter the Qrcodes bring only those that have the userid same as your currently logged in user.

final QuerySnapshot result = await Future.value(Firestore.instance
  .collection("lockers")
  .where("userid", isEqualTo: "$codigoSalvoAposConexao").where("numero_serie", isEqualTo: "$_numeroSerie")
  .limit(1)
  .getDocuments()); // verifica no banco se existe

Note: I don’t remember if this is the correct way to make a filter composed of two fields in firebase.

If you want to know a little more about logging in the way I mentioned, take a look here which is well explained. (It is in English but it is easy to understand)

Edited

To perform the filter with limit that you want, I believe it is necessary to use the orderBy before. As I am without Flutter on my computer now, I can not be precise in the example, but try something like this:

final QuerySnapshot result = await Future.value(Firestore.instance
  .collection("lockers")
  .where("numero_serie", isEqualTo: "$_numeroSerie")
  .where("userid", isEqualTo: "$codigoSalvoAposConexao")
  .orderBy("userid")
  .limit(1)
  .getDocuments()); // verifica no banco se existe

Note: I believe the field used in orderBy should be the same as where preceding.