javascript - 我在 deviceToken.then.result (/srv/index.js :14:33)"at node. js

Question

这是我的代码:

    const deviceToken = admin.database().ref(`/users/{sender_user_id}/token_id`).once('value');

    return deviceToken.then(result => {
        const token_id = result.after.data();

        const payload = {
            notification: {
                title: "New message!",
                body: "You have a new message!",
                icon: "default"
            }
        };

        return admin.messaging().sendToDevice(token_id, payload).then(response => {
            return console.log('This was a notification');

        });
    });


});

我收到此错误:

TypeError: Cannot read property 'data' of undefined at deviceToken.then.result (/srv/index.js:14:33)

我要从用户那里检索设备 token ID。我该怎么做？

节点--版本:v12.4.0 npm --版本:6.9.0

Answer 1

once 里面的方法 firebase.database.Reference 返回 Promise<DataSnapshot> 。类(class) admin.database.DataSnapshot 不包含名为 after 的属性。如果您尝试检索 token从数据库中然后更改以下内容:

    return deviceToken.then(result => {
        const token_id = result.after.data();

进入此:

    return deviceToken.then(result => {
        const token_id = result.val();

来自文档:

val

Extracts a JavaScript value from a DataSnapshot.

Depending on the data in a DataSnapshot, the val() method may return a scalar type (string, number, or boolean), an array, or an object. It may also return null, indicating that the DataSnapshot is empty (contains no data).