Firebase数据库递增一个int [英] Firebase database increment an int

问题描述

要在数据库中递增一个int值，我首先使用侦听器获取该值，将其递增1，然后将新值设置为数据库.这可行，但是我想知道是否有更简单的方法可以做到这一点.这样看来工作量太大.

For incrementing an int value in my database , I first get that value by using a listener , increment it by 1 and then set the new value to database. This works but I want to know if there is an easier way of doing this. This way seems like too much work.

推荐答案

Firebase数据库中没有服务器端增加值(或执行其他计算)的方法.

There is no server-side way to increment values (or do other calculations) in the Firebase Database.

您的方法是做到这一点的一种方法，但它有可能导致比赛状态.

Your approach is one way of doing this, but it has the chance of leading to a race condition.

1. 数据库中的值为12
2. 客户端1读取值12
3. 客户端2读取值12
4. 客户端1写入其增量值13
5. 客户端2写入其增量值13

现在结果可能不正确(取决于您的用例).

The result is now likely incorrect (it depends on your use-case).

在这种情况下，使其工作的一种方法是使用Firebase事务，该事务将读取和写入结合为一个功能.

In that case, one way to make it work is to use Firebase transactions, which combine the reading and writing into a single function.

Firebase数据库文档中介绍了交易. .我强烈建议您阅读.在那儿花几个小时可以避免很多问题.从文档中:

Transactions are covered in the Firebase Database documentation. I highly recommend reading it. A few hours spent there will prevent many problems down the road. From the docs:

postRef.runTransaction(new Transaction.Handler() {
    @Override
    public Transaction.Result doTransaction(MutableData mutableData) {
        Long value = mutableData.getValue(Long.class);
        if (value == null) {
            mutableData.setValue(0);
        }
        else {
            mutableData.setValue(value + 1);
        }

        return Transaction.success(mutableData);
    }

    @Override
    public void onComplete(DatabaseError databaseError, boolean b,
                           DataSnapshot dataSnapshot) {
        Log.d(TAG, "transaction:onComplete:" + databaseError);
    }
});

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