我需要同步所有结果，并使用 async/await 关键字（如 c#）附加到字符串。
我是 Node.js 新手，我无法将这种新语法适应我的代码。
var string1 = '';
var string2 = '';
var string3 = '';
var string4 = '';
DatabasePool.getConnection(function(err, connection) {
connection.query(query,function (err, result) {
if (err){};
string1 = result;
});
connection.query(query,function (err, result) {
if (err){};
string2 = result;
});
connection.query(query,function (err, result) {
if (err){};
string3 = result;
});
connection.query(query,function (err, result) {
if (err){};
string4 = result;
});
//I need to append all these strings to appended_text but
//all variables remain blank because below code runs first.
var appended_text = string1 + string2 + string3 + string4;
});
如果您碰巧在 Node 8+ 中，您可以利用本机
util.promisify()不要忘记用
bind()thisconst mysql = require('mysql'); // or use import if you use TS
const util = require('util');
const conn = mysql.createConnection({yourHOST/USER/PW/DB});
// node native promisify
const query = util.promisify(conn.query).bind(conn);
(async () => {
try {
const rows = await query('select count(*) as count from file_managed');
console.log(rows);
} finally {
conn.end();
}
})()
使用mysql2包。它有承诺包装，所以你可以这样做：
async function example1 () {
const mysql = require('mysql2/promise');
const conn = await mysql.createConnection({ database: test });
let [rows, fields] = await conn.execute('select ?+? as sum', [2, 2]);
}
假设你使用的 ORM 是基于承诺的，你可以做这样的事情
async function buildString() {
try {
const connection = await DatabasePool.getConnection();
const string1 = await connection.query(query);
const string2 = await connection.query(query);
const string3 = await connection.query(query);
const string4 = await connection.query(query);
return string1 + string2 + string3 + string4;
} catch (err) {
// do something
}
}
任何 Promise 都可以通过将
awaitasynctry/catch我还想指出，这 4 个查询不是同时运行。为此，您仍然需要使用 Promise.all。
如果你想使用mysql（也称为mysqljs），如果你不想使用包装器，你必须做一些工作。但这很容易。连接函数如下所示：
const mysql = require('mysql')
var my_connection = mysql.createConnection({ ... })
async function connect()
{
try
{
await new Promise((resolve, reject) => {
my_connection.connect(err => {
return err ? reject(err) : resolve()
})
})
}
catch(err)
{
...handle errors...
}
}
connect()
如您所见，等待将知道如何处理承诺。您创建此类并在回调实现中使用解析/拒绝函数。这就是它的全部内容，真的，所以使用包装器可能有点多，除非您经常访问数据库。
或者使用mysql-async-simple
https://www.npmjs.com/package/mysql-async-simple
const { makeDb } = require('mysql-async-simple');
const mysql = require("mysql");
const connection = mysql.createConnection({
host: process.env.HOST,
user: process.env.USER,
password: process.env.PASSWORD,
database: process.env.DB
});
const db = makeDb();
await db.connect(connection);
try {
const users = await db.query(connection, 'SELECT * FROM users');
} catch (e) {
// handle exception
} finally {
await db.close(connection);
}正如LeOn - Han Li所述，我进行了一些小的修改，因为我必须处理结果。
var mysql = require('mysql');
const util = require('util');
const conn = mysql.createConnection({
host : '127.0.0.1',
user : 'user',
password : 'password',
database : 'database'
});
const query = util.promisify(conn.query).bind(conn);
let result = async function() {
var userCourse = [];
try {
const rows = await query('select * as count from file_managed');
} finally {
conn.end();
return userCourse;
}
};
result()
.then(value => {
console.log(value)
});
promise-mysqlconst mysql = require('promise-mysql')
const getDbConnection = async () => {
return await mysql.createConnection({
host: process.env.HOST,
user: process.env.USER,
password: process.env.PASSWORD,
database: process.env.DB
})
}
const getUsers = async () => {
const db = await getDbConnection()
const users = await db.query("SELECT * FROM users")
await db.end()
return users
}
您必须确保您使用的 mysql 库支持 Promises，这是
asyncawaitpromisifyAllasync function appendedText() {
const connection = await DatabasePool.getConnectionAsync();
const [string1, string2, string3, string4] = await [
connection.query(query1),
connection.query(query2),
connection.query(query3),
connection.query(query4),
];
return string1 + string2 + string3 + string4;
}
请注意，调用
appendedText()appendedText().then(appended_text => {});
const { makeDb } = require('mysql-async-simple');
const mysql = require("mysql");
const connection = mysql.createConnection({
host: process.env.HOST,
user: process.env.USER,
password: process.env.PASSWORD,
database: process.env.DB
});
const db = makeDb();
await db.connect(connection);
try {
const users = await db.query(connection, 'SELECT * FROM users');
} catch (e) {
// handle exception
} finally {
await db.close(connection);
}我们可以在 mysql.connect 中实现 Promise，而不是使用 util 或 promise/mysql
var con = require('mysql');
var mysql = con.createConnection({
host: "localhost",
user: "root",
password: "pass",
database: "test"
});
async function asyncAwait(req, res) {
var promise1;
mysql.connect((err) => {
promise1 = new Promise((resolve, reject) => {
console.log('Mysql: Connected');
resolve(response.write(uc.upperCase('Connected\n')));
});
promise1
.then(() => {
//Implement the logic here
})
.catch(error => {
console.log(error)
});
})
}
await asyncAwait();
就我而言，我必须创建一个辅助函数，它是一个承诺并解决如下
const mysqlQuery = async (connection, queryConfig) => {
const config = { ...queryConfig, timeout: 4000 }
return new Promise((resolve, reject) => {
return connection.query(config, function (error, results, fields) {
if (error) {
reject(error);
}
resolve(results);
});
})
}
现在我可以轻松使用上面的内容了
const response = await mysqlQuery(connection, {
sql: 'SELECT * FROM `user`',
});
console.log(response)
连接是你的mysql连接，如下所示
var connection = mysql.createConnection({
host,
user, //
password, //
database,
port
})
connection.connect(async (err) => {
if(err){
//connection error
return;
}
//successifull connection
})
我正在使用以下mysql2：
const express = require('express');
const cors = require('cors');
const mysql = require("mysql2/promise");
const fetch = require('node-fetch');
所以它仍然不适用于上面提到的代码。我会尝试续集，看看是否有效。