从Firebase云函数返回的值或对象始终为null

Question

我使用以下代码从Firebase返回一个对象，但值始终为null。

这是我的Firebase云功能：

exports.useVoucher = functions.https.onCall((data, context) => {
const type = data.type
const voucher_code = data.voucher_code
const current_time = data.current_time
console.log("useVoucher type is ", type + " and voucher_code is ", voucher_code)
return admin.database().ref().child("vouchers").child(voucher_code).once("value").then((snapshot) => {
if (snapshot.exists()) {
console.log("useVoucher snapshot is ", snapshot.val());
if (snapshot.val()[type] === true) {
let path = "vouchers/" + voucher_code + "/" + type
admin.database().ref().update({
[[path]]: current_time
}, error => {
if (error) {
console.log("useVoucher failed")
return {is_valid: false}
} else {
console.log("useVoucher succeeded")
return {is_valid: true}
}
})
} else {
console.log("useVoucher voucher found but type not found or not true")
return {is_valid: false}
}
} else {
console.log("useVoucher voucher_code is not valid");
return {is_valid: false}
}
})
})

这就是我称之为客户端的方式(我删除了一些无关的代码(：

async function testVoucher(type) {
const voucher_code = input_text.value.trim()
console.log("submitVoucher voucher_code is ", voucher_code + " type is ", type)
let current_time = Number(new Date())
console.log("submitVoucher current_time is ", current_time)
await useVoucher({ type: type, voucher_code: voucher_code, current_time: current_time })
.then((res) => {
console.log("submitVoucher res is ", res)
let data = res.data
console.log("submitVoucher data is ", data)
})
.catch((error) => {
console.log("submitVoucher error is ", error)
})
}

不管云函数走哪条路径，它总是返回"；res为null"为什么？

Answer 1

您的问题有两个潜在原因：

1. 你不会把承诺挂在链子上。更确切地说，您不会返回admin.database().ref().update(...);返回的Promise。这行前面应该有一个return
2. 如果更新成功，您实际上不会返回任何内容。事实上，即使在这一行前面添加return，在出现错误的情况下也只会返回，而在成功的情况下则不会返回：admin.database().ref().update({...}, error => { **You only return here**})

由于使用了几个if块，因此使用async/await更容易。以下应该可以做到(未经测试(：

exports.useVoucher = functions.https.onCall(async (data, context) => {   // See async keyword
try {
const type = data.type
const voucher_code = data.voucher_code
const current_time = data.current_time
console.log("useVoucher type is ", type + " and voucher_code is ", voucher_code)
const snapshot = await admin.database().ref().child("vouchers").child(voucher_code).get();
if (snapshot.exists()) {
console.log("useVoucher snapshot is ", snapshot.val());
if (snapshot.val()[type] === true) {
let path = "vouchers/" + voucher_code + "/" + type
await admin.database().ref().update({
[[path]]: current_time
});
return { is_valid: true }
} else {
console.log("useVoucher voucher found but type not found or not true")
return { is_valid: false }
}
} else {
console.log("useVoucher voucher_code is not valid");
return { is_valid: false }
}
} catch (error) {
console.log(error);
// Important: Look in the doc how to deal with an error in a Callable Cloud Function.
//https://firebase.google.com/docs/functions/callable#handle_errors
}
});

---

请注意，我们使用get()方法。once("value")是正确的，但使用get()更清晰可读(get()对于客户端SDK还有一些其他优势，请参阅文档(。

Answer 2

您可以尝试将云函数包装为promise，以便在执行完成时返回resolve和reject的回调。

exports.useVoucher = functions.https.onCall((data, context) => {
const type = data.type
const voucher_code = data.voucher_code
const current_time = data.current_time
console.log("useVoucher type is ", type + " and voucher_code is ", voucher_code)
return new Promise(function (resolve, reject) {
admin.database().ref().child("vouchers").child(voucher_code).once("value").then((snapshot) => {
if (snapshot.exists()) {
console.log("useVoucher snapshot is ", snapshot.val());
if (snapshot.val()[type] === true) {
let path = "vouchers/" + voucher_code + "/" + type
admin.database().ref().update({
[[path]]: current_time
}, error => {
if (error) {
console.log("useVoucher failed")
reject({ is_valid: false })
} else {
console.log("useVoucher succeeded")
resolve({ is_valid: true })
}
})
} else {
console.log("useVoucher voucher found but type not found or not true")
reject({ is_valid: false })
}
} else {
console.log("useVoucher voucher_code is not valid");
reject({ is_valid: false })
}
})
}

})