Firebase 实时数据库从已删除节点访问数据数组

Question

我正在删除一个 FRTDB 节点，我想从该节点访问已删除的数据。函数如下所示：

exports.events = functions.database.ref('/events/{eventId}').onWrite(async (change, context) => {
  const eventId = context.params.eventId
  if (!change.after.exists() && change.before.exists()) {
    //data removed
    return Promise.all([admin.database().ref(`/events/${eventId}/dayofweek`).once('value')]).then(n => {
      const pms = []
      const days = n[0]
      days.forEach(x => {
        pms.push(admin.database().ref(`${change.before.val().active ? 'active' : 'inactive'}/${x.key}/${eventId}`).set(null))
      })
      return Promise.all(pms)
    });
   else {
    return null;
  }
})

我遇到的问题是

admin.database().ref(`/events/${eventId}/dayofweek

不要循环数据，因为数据似乎不再存在，所以 forEach 无法正常工作。我怎样才能访问这些数据并循环删除的数据？

Answer 1

当然，您将无法读取刚刚删除的数据。该函数在删除完成后 运行。如果你想获得刚刚删除的数据，你应该使用 change.before 中描述的 documentation:

The Change object has a before property that lets you inspect what was saved to Realtime Database before the event. The before property returns a DataSnapshot where all methods (for example, val() and exists()) refer to the previous value. You can read the new value again by either using the original DataSnapshot or reading the after property. This property on any Change is another DataSnapshot representing the state of the data after the event happened.

Answer 2

从数据库中删除的数据实际上包含在对您的 Cloud Function 的调用中。你可以从 change.before.

得到 if

exports.events = functions.database.ref('/events/{eventId}').onWrite(async (change, context) => {
  const eventId = context.params.eventId
  if (!change.after.exists() && change.before.exists()) {
    //data removed
    days = change.before.val().dayofweek;
    ...
})

Firebase 实时数据库从已删除节点访问数据数组

Firebase real time database access data array from deleted node

javascript

firebase-realtime-database

google-cloud-functions

firebase-admin