Firestore FCM推送通知云功能-Android

Question

我正在搜索，但无法找到解决问题的方法，我需要一个示例，说明如何从云功能发送FCM消息，但是使用FIRESTORE，而不是数据库实时...

我需要查询“用户”文档，在该文档中我有令牌来发送消息...

const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp();

exports.sendNotificaction = functions.firestore
    .document('messages/{messageID}')
    .onCreate((snap, context) => {

    const message = snap.data();
    const messageType = message.type;
    const userID = message.userID;

    console.log(messageType);
    console.log(userID);

    // I NEED TO QUERY MY "USER" DOC WITH "userID" TO GET THE TOKEN

        //let token = 'eHQMpJkde_o:APA91bGa5x1lWB7kbK92QgCGkpyMq4PuQJA83_tIMIfzRil1Poly7ZzVVLU2Cs0GCTs77jgQo1i6Nn3vpzrMl6X2Zw9tN3eQIuJSvXuqgNUTa2EJEkKAbmqiVb2MGGHhPTanITJ0lCgaFpQkJjgznfd-MO2pv9S2PQ';

        let payload = {
            notification: {
                title: 'Notificacion from firebase',
                body: 'Test',
                sound: 'default',
                badge: '1'
            }
        };
        return admin.messaging().sendToDevice(token, payload);
    //}
    });