在Firebase中自动增加值

Question

如何从Android客户端自动增加存储在Firebase中的值？

目前:我宣布int id = 1.当我递增时,我看到存储的值2,3等.那没关系,但是当我重新运行项目时,id再次设置为1.

我希望它表现得像一个静态变量,所以我可以创建一个从1到无穷大而不重置的id.

更新失败

我使用以下内容将Firebase引用和字符串传递给函数incrementCounter.

if(language_chosen.equalsIgnoreCase("english"))
 {
   Firebase publRef = f.child("Language").child("English").child("Message");
   Firebase newPublRef = publRef.push();
   writeMsgActivity demo = new writeMsgActivity();
   demo.incrementCounter(newPublRef,the_msg_enter);                                 
  }

现在我尝试public void incrementCounter(Firebase publref,String my_msg)在oncomplete方法中使用传递的引用和字符串, 但它给了我一个错误.

   public void incrementCounter(Firebase publref,String my_msg) {
    publref.runTransaction(new Transaction.Handler() {
        @Override
        public Transaction.Result doTransaction(final MutableData currentData) {
            if (currentData.getValue() == null) {
                currentData.setValue(1);
            } else {
                currentData.setValue((Long) currentData.getValue() + 1);
            }

            return Transaction.success(currentData);
        }

        public void onComplete(FirebaseError firebaseError, boolean committed, DataSnapshot currentData) {
            if (firebaseError != null) {
                System.out.println("Firebase counter increment failed.");
            } else {
                System.out.println("Firebase counter increment succeeded.");

                Map<String, Object> publ = new HashMap<String, Object>();
                publ.put("pubMsg", my_msg);
                publ.put("id",currentData);
                publref.setValue(publ);
            }
        }
    });
}

更新已解决

                final Firebase upvoteref = new Firebase("https://shareurday.firebaseio.com/Message/"+msg_id+"/upvotes"); 

            upvoteref.runTransaction(new Transaction.Handler() {
                @Override
                public Transaction.Result doTransaction(final MutableData currentData) {
                    if (currentData.getValue() == null) {
                        currentData.setValue(1);
                    } else {
                        currentData.setValue((Long) currentData.getValue() + 1);
                    }
                    return Transaction.success(currentData);
                }

                public void onComplete(FirebaseError firebaseError, boolean committed, DataSnapshot currentData) {
                    if (firebaseError != null) {
                        System.out.println("Firebase counter increment failed.");
                    } else {
                        System.out.println("Firebase counter increment succeeded.");
                    }
                }
            });

变量msg_id是来自push的随机生成的id.

Answer 1

这是一个增加单个计数器的示例方法.关键的想法是,您要么创建条目(将其设置为1),要么改变现有条目.在此处使用事务可确保如果多个客户端同时尝试递增计数器,则所有请求最终都将成功.从Firebase文档(强调我的):

在处理可能被并发更新损坏的复杂数据时,请使用我们的事务功能

public void incrementCounter() {
    firebase.runTransaction(new Transaction.Handler() {
        @Override
        public Transaction.Result doTransaction(final MutableData currentData) {
            if (currentData.getValue() == null) {
                currentData.setValue(1);
            } else {
                currentData.setValue((Long) currentData.getValue() + 1);
            }

            return Transaction.success(currentData);
        }

        @Override
        public void onComplete(FirebaseError firebaseError, boolean committed, DataSnapshot currentData) {
            if (firebaseError != null) {
                Log.d("Firebase counter increment failed.");
            } else {
                Log.d("Firebase counter increment succeeded.");
            }
        }
    });
}

Answer 2

向 firestore 添加了一项新功能以自动增加值。就这么简单

document("fitness_teams/Team_1").
  updateData(["step_counter" : FieldValue.increment(500)])

参考链接：https : //firebase.googleblog.com/2019/03/increment-server-side-cloud-firestore.html

在我的项目中使用以下代码。

var firestore = Firestore.instance;
firestore.collection('student').document('attendance').updateData({'total_attendace': FieldValue.increment(1)});