如何将事务与 int 数据一起使用 - Firestore Flutter答案

【问题标题】：How to use transaction with int data - Firestore Flutter如何将事务与 int 数据一起使用 - Firestore Flutter
【发布时间】：2023-03-26 00:55:01
【问题描述】：

创建帐户后，用户的 Firestore 会创建一个字段，显示用户当前拥有的塑料数量。到目前为止，我有一个按钮可以使用用户的文本字段输入来更新该金额。我听说过一种叫做交易的东西，它显然允许一个人将输入金额添加到整体数据中以便显示？当用户输入新数量时，我将如何完成此操作？

代码：

database.dart


Future<void> userSetup(String displayName) async {
  int plastics = 0;
  final CollectionReference users =
      FirebaseFirestore.instance.collection('UserNames');
  FirebaseAuth auth = FirebaseAuth.instance;
  String uid = auth.currentUser.uid.toString();
  users.doc(uid).set({'displayName': displayName, 'uid': uid});

//This is the field for plastics amount starting at 0.
  users.doc(uid).update({'plastics': plastics});
  return;
}

我如何检索金额数据：


final firestore = FirebaseFirestore.instance;
    FirebaseAuth auth = FirebaseAuth.instance;
    Future<String> getPlasticNum() async {
      final CollectionReference users = firestore.collection('UserNames');

      final String uid = auth.currentUser.uid;

      final result = await users.doc(uid).get();

      return result.data()['plastics'].toString();
    }

我如何显示它：


FutureBuilder(
          future: getPlasticNum(),
          builder: (_, AsyncSnapshot snapshot) {
            if (snapshot.connectionState == ConnectionState.waiting) {
              return Center(child: CircularProgressIndicator());
            }
            return Text(snapshot.data,
                style: TextStyle(color: Colors.amber[400], fontSize: 20));
          },
        ),

目前用户如何替换金额，但不能添加（问题）


OnPressed: () async {
                    try {
                      final String uid = auth.currentUser.uid;
                      FirebaseFirestore.instance
                          .collection('UserNames')
                          .doc(uid)
                          .update({
                        "plastics": int.parse(_plasticController.text),
                      });
                      Navigator.of(context).pop();
                    } catch (e) {}
                  },

【问题讨论】：

标签： firebase flutter google-cloud-firestore

【解决方案1】：

我做了一个单独的未来来处理添加：

final firestore = FirebaseFirestore.instance; //
FirebaseAuth auth = FirebaseAuth.instance;

Future<bool> addPlastic(String amount) async {
  try {
    String uid = auth.currentUser.uid;
    var value = double.parse(amount);
    DocumentReference documentReference =
        FirebaseFirestore.instance.collection('UserNames').doc(uid);

    FirebaseFirestore.instance.runTransaction((transaction) async {
      DocumentSnapshot snapshot = await transaction.get(documentReference);
      if (!snapshot.exists) {
        documentReference.set({'plastics': value});
        return true;
      }
      double newAmount = snapshot.data()['plastics'] + value;
      transaction.update(documentReference, {'plastics': newAmount});
      return true;
    });
  } catch (e) {
    return false;
  }
}

然后我只是在按下按钮时调用它

onPressed(){
addPlastics(_plasticController.text);
}

【讨论】：