在 Firebase 中自动增加一个值 [英] Auto-increment a value in Firebase

问题描述

如何从 Android 客户端自动递增 Firebase 中存储的值?

How do I auto increment a value stored in Firebase from an Android client?

目前:我声明 int id = 1.当我递增时，我看到值 2、3 等被存储.这很好，但是当我重新运行该项目时，id 再次设置为等于 1.

Currently: I declare int id = 1. When I increment, I see the values 2, 3 etc. being stored. That's fine, but when I re-run the project, id is set equal to 1 again.

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 到无穷大的 id，而无需重置.

I want it to behave like a static variable, so I can create an id which will go from 1 to infinity without resetting.

更新失败

我使用以下代码将 Firebase 引用和一个字符串传递给函数 incrementCounter.

I used the following to pass the Firebase reference and a string to the function 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);                                 
  }

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

Now I try to use the passed reference and string at public void incrementCounter(Firebase publref,String my_msg) in the oncomplete method but it gives me an error.

   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 是从推送中随机生成的 id.

The variable msg_id is the random generated id from push.

推荐答案

这是一个递增单个计数器的示例方法.关键思想是您要么创建条目(将其设置为等于 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增加计数器，则所有请求最终都会成功.来自 Firebase 文档(重点是我的):

Here's an example method that increments a single counter. The key idea is that you are either creating the entry (setting it equal to 1) or mutating the existing entry. Using a transaction here ensures that if multiple clients attempt to increment the counter at the same time, all requests will eventually succeed. From the Firebase documentation (emphasis mine):

在处理复杂数据时使用我们的事务功能并发更新可能会损坏

Use our transactions feature when working with complex data that could be corrupted by concurrent updates

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.");
            }
        }
    });
}

这篇关于在 Firebase 中自动增加一个值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！