[英]async await calling function node.js
我有這個 function,它查詢我的數據庫,然后調用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,我有這個:
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,發生的是這一行: rows[i]["NUM_OF_SESSIONS_PER_MONTH"] = (parseInt(rows[i]["NUM_OF_SESSIONS_PER_MONTH"]) - numOfSessionsLeft.numberOfSessionsLeftIs)
實際上是將0
分配給rows[i]["NUM_OF_SESSIONS_PER_MONTH"]
因為該變量賦值發生在 function 調用getNumOfSessionForTrainerClientList
完成之前。 所以它的發生不同步。 我不確定如何解決這個問題,我之前遇到過async
await
的問題,但沒有遇到過這樣的問題。 將不勝感激幫助。
For 循環本質上是同步的,因此不會等待您的方法getNumOfSessionForTrainerClientList
返回以繼續迭代。
正確的做法是:
getNumOfSessionForTrainerClientList
調用時使用 await() 。getNumOfSessionForTrainerClientList
應該返回 promise。樣本:
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 應該是這樣的:
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參數調用functionA()
。
您調用包含異步代碼的 function 因此 getNumOfSessionForTrainerClientList 不依賴於上面的代碼(以(行[i] [“NUM_OF 和控制台”開頭)你應該做的是
通過返回 prom 使 function 異步
使用 await 關鍵字執行它
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() })
}
對於 (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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