我编写了这个firebase函数，当数据被添加时触发，它汇总子值并更新总值字段。

export const updateTotalAnswersCounts = functions.database
    .ref('/CurrentGame/answers/{aid}').onWrite((change, context) => {
    var collectionRef = change.after.ref.parent;
    let total = 0;
     collectionRef.once('value',(snapshot)=>{
        console.log('snapshot',snapshot.val())
        snapshot.forEach((childSnapshot)=>{
            if(childSnapshot.val()!=null){
                console.log('childSnapshot',childSnapshot.val())
                total+=Number(childSnapshot.val())
            }
            return false;
        })
        const updates = {}
        updates['/totalAnswersCount'] = total;
        firebase.ref('/CurrentGame').update(updates)

    })

    return true;

});

当我添加新值到'answers'节点时，函数trigger工作，然后它获取所有数字（在此照片中为1+2+11），然后它将totalAnswersCount更新为sum = 14。
该加法操作

addAnswer() {
    let answer = 3;
    let userInfo = {
        uid: this.uid, 
        gid: '1',
        qid: '2',
        aid: '3'
    }
    const answer_ref = firebase.database().ref(`CurrentGame/answers/${answer}`);
    const users_answers_ref = firebase.database().ref(`GameQuestionStats/${this.user.uid}/${userInfo.qid}`);

    // Return the promise from countRef.transaction() so our function
    // waits for this async event to complete before it exits.
    return answer_ref.transaction((current) => {
        return (current || 0) + 1;
    }).then(() => {
        return users_answers_ref.set(userInfo,{merge:true})
    });
}

此Firebase函数交替工作
1.当我第一次加载应用程序时，它节点更新，而不做任何更新。
1.有时它具有延迟并且在3-4秒之后更新。
1.有时它真实的更新并且工作良好。