firebase云功能事务偶尔工作

Question

我有这样的云功能:

exports.updateNewsCount = functions.database.ref('/channels/{channelId}/news/{newsId}/') 
.onWrite (event => {
    const channelId = event.params.channelId;
    const newsId = event.params.newsId;
    let CntRef = admin.database().ref('/channelDetails/' + channelId + '/newsCnt');
    if (event.data.exists() && !event.data.previous.exists()){
        return CntRef.transaction(function(current){
            if (current){
                console.log ('current is not null');
                return (current || 0) + 1;
            }
            else {
                console.log('current is null');
                return current;
            }
        },function(error, b, d){
            if (error) 
                console.log(error);
            else 
                console.log ('error is null');
            if (b)
                console.log('boolean is true');
            else
                console.log('boolean is false');

            if (d)
                console.log('snapshot is ' + d);
            else
                console.log ('snapshot is null');
        }).then(()=>{});
    } else if (!event.data.exists() && event.data.previous.exists()){
        return CntRef.transaction(function(current){
            if (current)
                return (current || 1) - 1;
            else
                return current;
        }, function(error, b, d){if (error) console.log(error); if (d) console.log(d);}).then(()=>{});
    }
});

当我看到日志条目时，它会持续触发。但是，newsCnt 字段并未按预期更新。有时更新有时不更新!!!我在这里做错了什么？

Answer 1

您应该预料到一个事务可能会被多次调用，第一次时为 null。这就是交易的运作方式。请阅读文档here .

特别注意该部分中的以下标注:

Note: Because your update function is called multiple times, it must be able to handle null data. Even if there is existing data in your remote database, it may not be locally cached when the transaction function is run, resulting in null for the initial value.