[英]Array push gives empty result node js
我正在創建一個 API 用於列出帶有圖像的行程數據和 pdf 基礎 url,一切正常,但我無法訪問循環的最后一個結果數組data_to_send
。
應用程序.js
app.get("/getChallanList/:userId/:role", (req, res) => {
const userData = req.params;
let site_source = "";
let site_destination = "";
var site_from_name = "";
const data_to_send = [];
if (userData.role == "D") {
db.select("trip", "*", `driver_id = '${req.params.userId}'`, (data) => {
for (let i = 0; i < data.data.length; i++) {
site_source = data.data[i].site_from;
site_destination = data.data[i].site_to;
db.select(
"site",
"*",
`id in ('${site_source}','${site_destination}')`,
(data_site) => {
data.data[i].site_from = data_site.data[0].name;
data.data[i].site_to = data_site.data[1].name;
if (data.data[i].truck_challan_pdf != "") {
data.data[i].truck_challan_pdf =
base_url + "truckchallan/" + data.data[i].truck_challan_pdf;
}
if (data.data[i].driver_challan_pdf != "") {
data.data[i].driver_challan_pdf =
base_url + "driverchallan/" + data.data[i].driver_challan_pdf;
}
if (data.data[i].preparer_img != "") {
data.data[i].preparer_img = base_url + data.data[i].preparer_img;
}
if (data.data[i].driver_img != "") {
data.data[i].driver_img = base_url + data.data[i].driver_img;
}
data_to_send.push(data.data);
// console.log(data_to_send); // working
}
);
}
console.log(data_to_send); // empty
});
}
}
db.select
let select = (table, column, condition, callback) => {
try {
let sql = "SELECT " + column + " FROM " + table + " WHERE " + condition;
conn.query(sql, (err, results) => {
if (err) {
let data = {
status: 0,
data: sql,
message: "Something went wrong!",
};
callback(data);
} else {
let data = {
status: 1,
data: results,
message: "Success",
};
callback(data);
}
});
} catch (err) {
let data = {
status: 0,
data: err,
message: "In catch",
};
callback(data);
}
};
異步等待
app.get("/getChallanList/:userId/:role", async (req, res) => {
const userData = req.params;
let site_source = "";
let site_destination = "";
var site_from_name = "";
const data_to_send = [];
if (userData.role == "D") {
await db.select(
"trip",
"*",
`driver_id = '${req.params.userId}'`,
async (data) => {
// const data_to_send_ = [];
for (let i = 0; i < data.data.length; i++) {
site_source = data.data[i].site_from;
site_destination = data.data[i].site_to;
await db.select(
"site",
"*",
`id in ('${site_source}','${site_destination}')`,
(data_site) => {
data.data[i].site_from = data_site.data[0].name;
data.data[i].site_to = data_site.data[1].name;
if (data.data[i].truck_challan_pdf != "") {
data.data[i].truck_challan_pdf =
base_url + "truckchallan/" + data.data[i].truck_challan_pdf;
}
if (data.data[i].driver_challan_pdf != "") {
data.data[i].driver_challan_pdf =
base_url + "driverchallan/" + data.data[i].driver_challan_pdf;
}
if (data.data[i].preparer_img != "") {
data.data[i].preparer_img =
base_url + data.data[i].preparer_img;
}
if (data.data[i].driver_img != "") {
data.data[i].driver_img = base_url + data.data[i].driver_img;
}
data_to_send.push(data.data);
// console.log(data_to_send); // working
}
);
// data_to_send_.push(data_to_send);
}
console.log(data_to_send); // empty
}
);
}
}
這是因為 NodeJs 的異步行為,所以你必須相應地計划事情,即
console.log(1)
db.select(
"trip",
"*",
`driver_id = '${req.params.userId}'`,
async (data) => {
console.log(2)
})
console.log(3)
上述代碼的 output 將是 1,然后是 3,然后是 2,這就是 NodeJs 的工作方式,它不等待 I/O 調用,即在您的情況下是 DB 查詢。 請查看 Promise 在 NodeJs 中的工作方式以獲取更多詳細信息。 以下是完成任務的方法:
const challanList = (userData) => {
return new Promise((resolve, reject) => {
const data_to_send = [];
db.select("trip", "*", `driver_id = '${req.params.userId}'`, data => {
for (let i = 0; i < data.data.length; i++) {
const site_source = data.data[i].site_from;
const site_destination = data.data[i].site_to;
db.select("site", "*", `id in ('${site_source}','${site_destination}')`, data_site => {
data.data[i].site_from = data_site.data[0].name;
data.data[i].site_to = data_site.data[1].name;
if (data.data[i].truck_challan_pdf != "") {
data.data[i].truck_challan_pdf = base_url + "truckchallan/" + data.data[i].truck_challan_pdf;
}
if (data.data[i].driver_challan_pdf != "") {
data.data[i].driver_challan_pdf = base_url + "driverchallan/" + data.data[i].driver_challan_pdf;
}
if (data.data[i].preparer_img != "") {
data.data[i].preparer_img = base_url + data.data[i].preparer_img;
}
if (data.data[i].driver_img != "") {
data.data[i].driver_img = base_url + data.data[i].driver_img;
}
data_to_send.push(data.data);
// console.log(data_to_send); // working
});
}
resolve(data_to_send);
});
});
};
app.get("/getChallanList/:userId/:role", async (req, res) => {
const userData = req.params;
const challanListResult =await challanList(userData);
console.log(challanListResult);
resp.json(challanListResult);
});
在不知道您正在使用什么數據庫或 ORM 的情況下很難回答,但我懷疑db.select
是一種異步方法,即它返回一個Promise
如果是這樣,第二個控制台日志仍然看到“舊” data_to_send
。
嘗試在第一個db.select
調用之前添加await
。 (不要忘記app.get
的第二個參數中回調前面的async
。
您的數據庫是異步的,因此console.log(data_to_send)
在查詢完成執行之前被調用。 嘗試在第 1 行的(req, res)
之前添加async
,然后在await
之前db.select
。
這對我有用
app.get("/getChallanList/:userId/:role", async (req, res) => {
const userData = req.params;
let site_source = "";
let site_destination = "";
var site_from_name = "";
const data_to_send = [];
if (userData.role == "D") {
const data = await db.query(
`SELECT * FROM trip WHERE driver_id = '${req.params.userId}'`
);
// console.log(data.length);
// const data_to_send_ = [];
for (let i = 0; i < data.length; i++) {
site_source = data[i].site_from;
site_destination = data[i].site_to;
// cons
const site_data = await db.query(
`SELECT * FROM site WHERE id in ('${site_source}','${site_destination}')`
);
// console.log(site_data);
db.select(
"site",
"*",
`id in ('${site_source}','${site_destination}')`,
(data_site) => {
data[i].site_from = data_site.data[0].name;
data[i].site_to = data_site.data[1].name;
if (data[i].truck_challan_pdf != "") {
data[i].truck_challan_pdf =
base_url + "truckchallan/" + data[i].truck_challan_pdf;
}
if (data[i].driver_challan_pdf != "") {
data[i].driver_challan_pdf =
base_url + "driverchallan/" + data[i].driver_challan_pdf;
}
if (data[i].preparer_img != "") {
data[i].preparer_img = base_url + data[i].preparer_img;
}
if (data[i].driver_img != "") {
data[i].driver_img = base_url + data[i].driver_img;
}
data_to_send.push(data);
// console.log(data.data);
// console.log(data_to_send); // working
}
);
// data_to_send_.push(data_to_send);
}
// console.log(data_to_send);
// console.log(data_to_send);
res.send({ success: 1, data: data, message: "" });
}
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.