我正在學習 NodeJs 并且在使用 async/await 時遇到了一些問題。我正在使用 Firebase 資料庫來讀取/寫入資料。這就是我在做什么。（如果你需要它的完整功能）。
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';
}
當我嘗試處理一些資料并添加 Firebase 一次函式“異步”并在內部等待以將我需要的資料推送到陣列時，問題就出現了。然后回傳importList；什么都不回傳。我認為await refListGoods.once會導致這個問題。正如我所想，里面的 await 已經完成了它的職責，我可以在里面很好地 console.log importList 。但我認為await importRef.once也會在回傳之前完成。當我洗掉await refListGoods.once時，回傳很好，但我沒有得到我需要的資料。我是否需要像上面的findTypeAndColor 和 findUserName那樣重構所有代碼，或者有更好的方法來解決這個問題？
uj5u.com熱心網友回復：
如果要await在Promise回傳的 by上使用once，則不應將回呼函式傳遞給它。
所以而不是：
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;
});
做：
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;
}
})
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