如何在firebase函数中获取另一个文档的数据？

Question

如何在Firebase函数中获取Firestore数据？

  var number;
  await db.collection("users").doc(uid).collection("info").doc("info").get().then(doc => {
      number = doc.data().get("countUnMutable").toString;
      return db;
  });

我想使用接收到的值将文档写入其他地址，但是没有写入。

exports.changeLocation = functions.region('europe-west1').firestore.document('users/{userId}/firstNotes/{noteId}').onCreate(async (snap,context) => {
  const uid = context.params.userId;
  const data = snap.data();
  const noteId = context.params.noteId;
  var number;
  await db.collection("users").doc(uid).collection("info").doc("info").get().then(doc => {
      number = doc.data().get("countUnMutable").toString;
      return db;
  });

  await db.collection('users').doc(uid).collection("notes").doc("firebaseNote:".concat(number)).set(data);

  const alreadyExistedDocument = db.collection('users').doc(uid).collection('notes').doc(noteId);
  await alreadyExistedDocument.delete();
});