Firebase Cloud函数onWrite获取所有新条目

Question

此events函数在第一次添加数据时有效，但在添加其他条目时，change.after.val()将返回所有条目，而不仅仅是新条目。

我可以以某种方式获取所有新条目或我必须fcm/{pushId}/{uid}，获取每个用户ID并将其发送到sendNotification吗？

exports.events = functions.database.ref('/fcm/{pushId}')
    .onWrite((change, context) => {

        // Exit when the data is deleted.
        if (!change.after.exists()) {
            return null;
        }

        const eventId = context.params.pushId;
        const dsnap = change.after.val();

        let guests = Object.keys(dsnap);

        const promises = guests.map((data) => admin.database()
            .ref('playerIds')
            .child(data)
            .once('value'));

        return Promise.all(promises).then(data => {

            return data.map(item => {
                let itemVal = Object.keys(item.val());
                return itemVal;
            })
        }).then((itemVal) => {

            if (itemVal) {
                console.log('itemVal', itemVal)
                admin.database().ref(`/events/${eventId}/`)
                    .once('value')
                    .then(event => {
                        if (event) {


                            let playerIds = [];

                            for (let id of itemVal) {
                                playerIds.push(id[0]);
                            }

                            let msg = "Your invitation has arrived!";

                            var eventObject = { "eventKey": eventId, "event": event };
                            sendNotification(playerIds, msg, eventObject);
                        }
                    })
            }

        });

    });

数据库模型：

fcm
  Eventid1
      UID1: true,
      UID2: true
  Event2
      UID2: true,
      ...