[英]async await calling function node.js
我有这个 function,它查询我的数据库,然后调用getNumOfSessionForTrainerClientList
function:
var select = "select * from USERS WHERE ASSIGNED_TRAINER = ?"
mysqlconn.connect(function(err) {
if (err) {
console.error('Database connection failed: ' + err.stack);
return;
}
mysqlconn.query(select, [req.session.username], async function(err, rows) {
if (err) {
console.log(err);
} else {
let numOfSessionsLeft = {
numberOfSessionsLeftIs: 0
}
for (var i = 0; i < rows.length; i++) {
getNumOfSessionForTrainerClientList(req, res, rows[i], numOfSessionsLeft)
rows[i]["NUM_OF_SESSIONS_PER_MONTH"] = (parseInt(rows[i]["NUM_OF_SESSIONS_PER_MONTH"]) - numOfSessionsLeft.numberOfSessionsLeftIs)
console.log(numOfSessionsLeft)
}
}
mysqlconn.end();
})
})
然后在 function getNumOfSessionForTrainerClientList
里面,我有这个:
async function getNumOfSessionForTrainerClientList(req, res, rows, numOfSessionsLeft) {
var getNumOfSessionForTrainerClientList = "select * from SCHEDULE WHERE CLIENT_USERNAME = ? AND ASSIGNED_TRAINER = ?"
mysqlconn.connect(async function(err) {
if (err) {
console.error('Database connection failed: ' + err.stack);
return;
}
mysqlconn.query(getNumOfSessionForTrainerClientList, [rows["USERNAME"], req.session.username], async function(err, sessionData) {
if (err) {
console.log(err);
} else {
numOfSessionsLeft.numberOfSessionsLeftIs = 1;
console.log(numOfSessionsLeft.numberOfSessionsLeftIs)
}
})
})
}
然而,发生的是这一行: rows[i]["NUM_OF_SESSIONS_PER_MONTH"] = (parseInt(rows[i]["NUM_OF_SESSIONS_PER_MONTH"]) - numOfSessionsLeft.numberOfSessionsLeftIs)
实际上是将0
分配给rows[i]["NUM_OF_SESSIONS_PER_MONTH"]
因为该变量赋值发生在 function 调用getNumOfSessionForTrainerClientList
完成之前。 所以它的发生不同步。 我不确定如何解决这个问题,我之前遇到过async
await
的问题,但没有遇到过这样的问题。 将不胜感激帮助。
For 循环本质上是同步的,因此不会等待您的方法getNumOfSessionForTrainerClientList
返回以继续迭代。
正确的做法是:
getNumOfSessionForTrainerClientList
调用时使用 await() 。getNumOfSessionForTrainerClientList
应该返回 promise。样本:
async function functionA() {
var select = "select * from USERS WHERE ASSIGNED_TRAINER = ?"
mysqlconn.connect(function(err) {
if (err) {
console.error('Database connection failed: ' + err.stack);
return;
}
mysqlconn.query(select, [req.session.username], async function(err, rows) {
if (err) {
console.log(err);
} else {
let numOfSessionsLeft = {
numberOfSessionsLeftIs: 0
}
for (var i = 0; i < rows.length; i++) {
await getNumOfSessionForTrainerClientList(req, res, rows[i], numOfSessionsLeft)
rows[i]["NUM_OF_SESSIONS_PER_MONTH"] = (parseInt(rows[i]["NUM_OF_SESSIONS_PER_MONTH"]) - numOfSessionsLeft.numberOfSessionsLeftIs)
console.log(numOfSessionsLeft)
}
}
mysqlconn.end();
})
})
}
你的 function getNumOfSessionForTrainerClientList 应该是这样的:
async function getNumOfSessionForTrainerClientList(req, res, rows, numOfSessionsLeft) {
return new Promise((resolve, reject) => {
var getNumOfSessionForTrainerClientList = "select * from SCHEDULE WHERE CLIENT_USERNAME = ? AND ASSIGNED_TRAINER = ?"
mysqlconn.connect(async function(err) {
if (err) {
console.error('Database connection failed: ' + err.stack);
return reject(err);
}
mysqlconn.query(getNumOfSessionForTrainerClientList, [rows["USERNAME"], req.session.username], async function(err, sessionData) {
if (err) {
console.log(err);
return reject(err);
} else {
numOfSessionsLeft.numberOfSessionsLeftIs = 1;
console.log(numOfSessionsLeft.numberOfSessionsLeftIs)
return resolve();
}
})
})
})
}
然后使用您需要的任何参数调用functionA()
。
您调用包含异步代码的 function 因此 getNumOfSessionForTrainerClientList 不依赖于上面的代码(以(行[i] [“NUM_OF 和控制台”开头)你应该做的是
通过返回 prom 使 function 异步
使用 await 关键字执行它
async function trainerClientList(){ return new Promise((resolve,reject)=>{ var getNumOfSessionForTrainerClientList = "select * from SCHEDULE WHERE CLIENT_USERNAME =? AND ASSIGNED_TRAINER =?" mysqlconn.connect(async function(err) { if (err) { console.error('Database connection failed: ' + err.stack); resolve() } mysqlconn.query(getNumOfSessionForTrainerClientList, [rows["USERNAME"], req.session.username], async function(err, sessionData) { if (err) { console.log(err); } else { numOfSessionsLeft.numberOfSessionsLeftIs = 1; console.log(numOfSessionsLeft.numberOfSessionsLeftIs) } }) }) resolve() })
}
对于 (var i = 0; i < rows.length; i++) { await trainerClientList() rows[i]["NUM_OF_SESSIONS_PER_MONTH"] = (parseInt(rows[i]["NUM_OF_SESSIONS_PER_MONTH"]) - numOfSessionsLeft.numberOfSessionsLeftIs) 控制台。日志(numOfSessionsLeft)}
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