为什么嵌套的异步/等待不能按预期工作？

Question

我正在学习NodeJ，并且在使用async/await时遇到了一些问题。我正在使用Firebase数据库读取/写入数据。我在做什么。(功能齐全，以备不时之需(。

async getImport(reqData: any): Promise<any> {
const username = 'kdat0310';
const db = admin.database();
const userRef = db.ref('/user');
const importRef = db.ref('/import');
const refAuthentication = db.ref('/Authentication');
const keyList = [];
const providerKey = [];
const khoList = [];
let index = 0;
const providerList = [];
const isValid = await refAuthentication.once('value', function (snapshot) {
for (const val of Object.values(snapshot.val())) {
if (
Object(val).username === Object(reqData).username &&
Object(val).token === Object(reqData).token
) {
return true;
}
}
return false;
});
if (isValid) {
await userRef.once('value', function (snapshot) {
for (const value of Object.values(snapshot.val())) {
if (value) {
if (Object(value).username == username) {
for (const val of Object(value).workAt) {
if (val) khoList.push(val.khoId);
}
}
}
}
});
const typeAndColorKey = [];
const typeAndColorValue = [];
const typeAndColorRef = db.ref('/TypeAndColor');
await typeAndColorRef.once('value', function (snapshot) {
let count = 0;
for (const key in snapshot.val()) {
typeAndColorKey.push(key);
}
for (const value of snapshot.val()) {
if (value !== undefined && value != null) {
typeAndColorValue.push({
id: typeAndColorKey[count],
type: value.type,
color: value.color,
});
count = count + 1;
}
}
});
const findTypeAndColor = (id: any) => {
for (const value of typeAndColorValue) {
if (id == value.id) {
return { type: value.type, color: value.color };
}
}
};
const userKey = [];
const userList = [];
await userRef.once('value', function (snapshot) {
let count = 0;
for (const key in snapshot.val()) {
userKey.push(key);
}
for (const value of Object(snapshot.val())) {
if (value != undefined && value != null) {
userList.push({
id: userKey[count],
name: Object(value).name,
});
count++;
}
}
});
const findUserName = (userId: any) => {
const returnValue = '';
for (const value of userList) {
if (userId == Object(value).id) {
return Object(value).name;
}
}
};
const importList = [];
await importRef.once('value', async function (snapshot) {
const importKey = [];
const cloneArr = snapshot.val().map((item: any) => {
return item;
});
for (const key in snapshot.val()) {
importKey.push(key);
}
let countTemp = 0;
for (const value of Object.values(cloneArr)) {
const goodsKeyList = [];
let count = 0;
if (khoList.indexOf(Object(value).warehouseId) !== -1) {
const listGoodsList = [];
if (Object(value).listGoods) {
for (const key in Object(value).listGoods) {
goodsKeyList.push(key);
}
const refListGoods = db.ref(
'/import/' + importKey[countTemp] + '/listGoods',
);
await refListGoods.once('value', function (snapshot) {
let item: any;
for (item of Object.values(snapshot.val())) {
if (item) {
const tempItem = item.filter((n: any) => n);
listGoodsList.push({
typeAndColor: findTypeAndColor(goodsKeyList[count]),
listGoods: tempItem,
number: tempItem.length,
});
}
count++;
}
});
}
console.log('test 1', listGoodsList);
if (listGoodsList !== []) {
importList.push({
listGoods: listGoodsList,
driver: Object(value).driver,
userId: Object(value).importEmployee,
name: findUserName(Object(value).importEmployee),
orderId: Object(value).orderId,
warehouseId: Object(value).warehouseId,
time: Object(value).time,
});
}
}
countTemp++;
}
console.log('test 2', importList);
});
return importList;
}
return 'Invalid';
}

问题出现在等待importRef.once当我试图处理一些数据并添加Firebase once函数"；异步；并在里面等待将我需要的数据推送到数组。然后返回importList不返回任何内容。我认为等待refListGoods.once会导致此问题。正如我所想，里面的等待已经完成了它的职责，我可以很好地安慰里面的.log importList。但我认为等待importRef.一次也会在返回之前完成。当我删除等待refListGoods时。一旦，返回是可以的，但我没有得到我需要的数据。我是否需要像上面的findTypeAndColor和findUserName那样重构所有代码，或者有更好的方法来解决这个问题？

Answer 1

如果要在once返回的Promise上使用await，则不应向其传递回调函数。

所以不是：

const isValid = await refAuthentication.once('value', function (snapshot) {
for (const val of Object.values(snapshot.val())) {
if (
Object(val).username === Object(reqData).username &&
Object(val).token === Object(reqData).token
) {
return true;
}
}
return false;
});

Do：

const snapshot = await refAuthentication.once('value');
let isValid = false;
snapshot.forEach((child) => {
const val = child.val();
if (val.username === Object(reqData).username &&
val.token === Object(reqData).token
) {
isValid = true;
}
})