[英]How to wait for this function to finish?
在將數據發送到控制台之前,我需要等待映射 function 完成。 我知道它與 Promise 有關。 我已經嘗試了幾個小時,即使在閱讀了很多關於 Promise 和異步函數的內容之后,我也無法讓它工作......
async function inactiveMemberWarner() {
var msg = "```javascript\nI have sent warnings to members that have been inactive for 2 weeks.\n\n"
var inactiveMembers = '';
var count = 0;
var guildMembers = client.guilds.find(g => g.name === mainGuild).members;
const keyPromises = await guildMembers.map(async (member) => {
if (isMod(member)) {
connection.query(`SELECT * from users WHERE userID='${member.id}'`, (err, data) => {
if (data[0]) {
if (!data[0].warnedForInactivity && moment().isSameOrAfter(moment(data[0].lastMSGDate).add('2', 'week'))) {
count++;
var updateWarning = {warnedForInactivity: 1}
connection.query(`UPDATE users SET ? WHERE userID='${data[0].userID}'`, updateWarning);
member.send(`**[*]** WARNING: You've been inactive on \`\`${mainGuild}\`\` for 2 weeks. Members that have been inactive for at least a month will be kicked.`);
inactiveMembers += `${count}. ${member.user.tag}\n`;
return inactiveMembers;
}
}
});
}
});
await Promise.all(keyPromises).then(inactiveMembersData => console.log(inactiveMembers)); // RETURNS AN EMPTY STRING
setTimeout(() => console.log(inactiveMembers), 5000); // RETURNS THE INACTIVE MEMBERS AFTER WAITING FOR 5 SECONDS (PRMITIVE WAY)
}
inactiveMemberWarner();
先感謝您!
你很近,但不完全在那里。
首先,一些注意事項:
await
可以用於任何值,但將它用於任何不是 Promise 的值是完全沒有意義的。 你的guildMembers.map(...);
返回一個數組,而不是 Promise。await
和.then(...)
有效,但有點混亂。 您已經在使用await
- 為什么還要處理回調?guildMembers.map(async...)
將確保所有請求或多或少立即被觸發,並且它們可以以任何順序完成。 這很好,但它是一種競爭條件,會導致或多或少隨機的結果順序。 您當前的代碼不起作用的原因是您的connection.query
function逃脫了異步控制流。 我的意思是,使用 async/await 和 Promises 的全部目的基本上是在本地跟蹤回調,並利用 promise 鏈接來動態添加回調。 如果您調用異步 function 並返回 Promise,您現在可以在代碼中的任何其他位置攜帶該await
並動態附加成功處理程序.then()
。
But the connection.query
function doesn't return a Promise, it just has you pass another naked callback - this one is not being tracked by a Promise, The Promise doesn't have a reference to that callback, it can't know when該回調被調用。 因此,您的 async/await 控制流被轉義,並且您的承諾在查詢運行之前很久就解決了。
您可以通過在異步 function 中創建新的 Promise 來解決此問題:
async function inactiveMemberWarner() {
var msg = "```javascript\nI have sent warnings to members that have been inactive for 2 weeks.\n\n"
var inactiveMembers = '';
var count = 0;
var guildMembers = client.guilds.find(g => g.name === mainGuild).members;
const keyPromises = guildMembers.map(async (member) => {
if (isMod(member)) {
return new Promise((resolve, reject) => {
connection.query(`SELECT * from users WHERE userID='${member.id}'`, (err, data) => {
if (err) reject(err); //make errors bubble up so they can be handled
if (data[0]) {
if (!data[0].warnedForInactivity && moment().isSameOrAfter(moment(data[0].lastMSGDate).add('2', 'week'))) {
count++;
var updateWarning = {warnedForInactivity: 1}
connection.query(`UPDATE users SET ? WHERE userID='${data[0].userID}'`, updateWarning);
member.send(`**[*]** WARNING: You've been inactive on \`\`${mainGuild}\`\` for 2 weeks. Members that have been inactive for at least a month will be kicked.`);
resolve(`${count}. ${member.user.tag}\n`;);
}
} else resolve(""); //make sure to always resolve or the promise may hang
});
});
}
});
let inactiveMembersData = await Promise.all(keyPromises); // Returns an array of inactive member snippets.
inactiveMembers = inactiveMembersData.join(""); //join array of snippets into one string
}
inactiveMemberWarner();
這會起作用,但是有一個更好的方法。 SQL 支持IN運算符,它允許您擁有WHERE userID IN (list_of_ids)
等條件。 換句話說,您可以在一個查詢中執行此操作。 您甚至可以指定更多條件,例如warnedForInactivity = 0
和lastMSGDate BETWEEN (NOW() - INTERVAL 14 DAY) AND NOW()
。 通過這種方式,您可以將所有當前處理邏輯卸載到 SQL 服務器上——您幾乎每次都應該嘗試這樣做。 它也會大大簡化這段代碼。 我不會再做 go 了,因為這個問題已經超出了 scope 的范圍,但如果你想不明白,請隨時問另一個。
我無法對此進行測試,但這通常對我有用的是當想要等待 smt 時:
async function inactiveMemberWarner() {
new Promise(function(cb,rj){
var msg = "```javascript\nI have sent warnings to members that have been inactive for 2 weeks.\n\n"
var inactiveMembers = '';
var count = 0;
var guildMembers = client.guilds.find(g => g.name === mainGuild).members;
const keyPromises = await guildMembers.map(async (member) => {
if (isMod(member)) {
connection.query(`SELECT * from users WHERE userID='${member.id}'`, (err, data) => {
if (data[0]) {
if (!data[0].warnedForInactivity && moment().isSameOrAfter(moment(data[0].lastMSGDate).add('2', 'week'))) {
count++;
var updateWarning = {warnedForInactivity: 1}
connection.query(`UPDATE users SET ? WHERE userID='${data[0].userID}'`, updateWarning);
member.send(`**[*]** WARNING: You've been inactive on \`\`${mainGuild}\`\` for 2 weeks. Members that have been inactive for at least a month will be kicked.`);
inactiveMembers += `${count}. ${member.user.tag}\n`;
cb(inactiveMembers);
}
}
});
}
});
cb('No Members');
}).then(inactiveMembersData => console.log(inactiveMembers)); // SHOULD RETURNS THE INACTIVE MEMBERS
}
inactiveMemberWarner();
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