云函数触发通知：TypeError: 'exists'

Question

我正在尝试让 Google firebase 云函数 codelab (https://codelabs.developers.google.com/codelabs/firebase-cloud-functions/#9) 与 Firestore 一起工作（现在它为实时数据库配置）。

我在修改 Firestore 的原始代码时遇到问题：

// Sends a notifications to all users when a new message is posted.
exports.sendNotifications = functions.database.ref('/messages/{messageId}').onCreate(
    async (snapshot) => {
      // Notification details.
      const text = snapshot.val().text;
      const payload = {
        }
      };
      // Get the list of device tokens.
      const allTokens = await admin.database().ref('fcmTokens').once('value');
      if (allTokens.exists()) {
        // Listing all device tokens to send a notification to.
        const tokens = Object.keys(allTokens.val());

        // Send notifications to all tokens.
        const response = await admin.messaging().sendToDevice(tokens, payload);
      }
    });

到目前为止我已经做了：

// Sends a notifications to all users when a new message is posted.
exports.sendNotifications = functions.firestore.document(‘/userscollection/{uid}').onCreate(
  async (snapshot) => {

// Notification details.
const text = snapshot.val().text;
const payload = {
notification: {
}
 };

    // Get the list of device tokens.    
const allTokens = await admin.firestore().collection('users').where('FCMToken', '>', "").get()
.then(snap =>{
if (snap.empty) {
console.log('snap is empty');
return;
}
snap.forEach(doc => {
console.log(doc.id, '=>', doc.data());
});
})
 .catch(err => {
console.log('Error getting docs', err);
});

console.log('allTokens is: ', allTokens);

    if (allTokens.exists()) {
      // Listing all device tokens to send a notification to.
      const tokens = Object.keys(allTokens.val());
      // Send notifications to all tokens.
      const response = await admin.messaging().sendToDevice(tokens, payload);
    }
  });

这个听/userscollection根集合正确所以触发云功能。但是控制台中的函数返回错误：TypeError: Cannot read property 'exists' of undefined at Object.<anonymous>

还有

console.log('allTokens is: ', allTokens); 

返回

allTokens is: undefined

在 Firestore 中，我将令牌存储在 /users 根集合中的用户文档中。所以我需要修改 codelab 以在 /users 集合中的所有用户文档中仅获取“token”字段。

有人帮忙吗？ 谢谢！

Answer 1

allToken 是undefined；它是对以下内容的评估：

const allTokens = await admin.firestore()
                    .collection('users')
                    .where('FCMToken', '>', "")
                    .get()
                    .then(snap => {
                      if (snap.empty) {
                        console.log('snap is empty');
                        return;
                      }
                    ); 

promise 解析为 undefined 值，因为在最后一个 thenable 是 return-ing undefined。

要纠正这个问题，您可以链接一个 thenable，从匹配的快照中的每个文档中获取令牌，返回-将其放入数组中。

const tokensFromQuerySnapshot = querySnapshot => {
  if(querySnapshot.empty) return [];

  const tokens = [];
  querySnapshot.forEach(queryDocumentSnapshot => {
    tokens.push(queryDocumentSnapshot.get('token'))
  });
  return tokens;
}

const allTokens = await admin.firestore()
                    .collection('users')
                    .where('FCMToken', '>', "")
                    .get()
                    .then(tokensFromQuerySnapshot);