如何让返回等待 MySQL 连接结束？节点.js

Question

我是 Node.js 的新手，我正在 Wix 上测试一些代码来检查我的数据库是否在允许创建新帐户名称之前已经存在（我故意不使用 WHERE 标记用于学习目的的时刻）。

当前方法检查帐户名称在连接完成之前返回，不允许正确进行检查。

任何帮助表示赞赏。

    export function tryToCreateAccount(login, password) 
{
    var mysql = require('mysql');

    var connection = mysql.createConnection({
        host: 'host',
        user: 'user',
        password: 'pass',
        database: 'db'
    });

    if(checkAccountName(login, connection))
    {
        console.log("Name didn't exist.");
    }
    else
    {
        console.log("Name Existed.");
    }
}

function checkAccountName(account_name, connection)
{
    var accountNameAvailable = true;

    connection.connect(function (err)
    {
        if(err) throw err;
        connection.query("SELECT login FROM accounts", function (err, result)
        {
            if (err) throw err;

            for(var i = 0; i < result.length ; i++)
            {
                if(result[i].login == account_name)
                {
                    console.log("Should of been false");
                    connection.end;
                    accountNameAvailable = false;
                }
            }

        });
        connection.end;
    });

    return accountNameAvailable;
}

Answer 1

我知道为什么它什么也没做，因为连接结束，下一个调用太晚了，而下一个在连接代码块内。

const mysql = require('mysql');
const connection = mysql.createConnection({
    host: 'host',
    user: 'user',
    password: 'pass',
    database: 'db'
});

export function tryToCreateAccount(login, password) 
{
    checkAccountName(login, connection, function(err, accountNameAvailable)
    {
      if(err || !accountNameAvailable){
        console.log("Name didn't exist.");
      }
      else
      {
        console.log("Name Existed.");
      }
   })
}

function checkAccountName(login, connection, next)
{
    var accountNameAvailable = false;

    connection.connect(function (err)
    {
        if(err) next(err);
        connection.query("SELECT login FROM accounts", function (err, result){
            if (err) next(err);
            for(var i = 0; i < result.length ; i++)
            {
                if(result[i].login == login)
                {
                    accountNameAvailable = true;
                }
            }
            next(null, accountNameAvailable);
            connection.end();
        });
    });
}

Answer 2

欢迎来到 Node.js（以及异步函数（和 Promises（和回调）的世界））

我以“回调”风格编写了此代码，但我强烈建议您研究 async/await 以了解此类内容，并了解“承诺”如何融入其中。

// to test, call tryToCreateAccount('login','pass',function(err,data){console.log(err,data)});

const mysql = require('mysql');
const connection = mysql.createConnection({
    host: 'host',
    user: 'user',
    password: 'pass',
    database: 'db'
});
export function tryToCreateAccount(login, password, next) 
{
    checkAccountName(login, connection, function(err, accountNameAvailable){
      if(err || !accountNameAvailable){
        console.log("Name didn't exist.");
        next(err || 'Name didn't exist.')
      }
      else
      {
        console.log("Name Existed.");
        next(null, true)
      }
   })
}

function checkAccountName(account_name, connection, next)
{
    var accountNameAvailable = false;

    connection.connect(function (err)
    {
        if(err) next(err);
        connection.query("SELECT login FROM accounts", function (err, result){
            if (err) next(err);
            for(var i = 0; i < result.length ; i++)
            {
                if(result[i].login == account_name)
                {
                    console.log("Should of been false");
                    connection.end;
                    accountNameAvailable = true;
                }
            }
            connection.end();
            next(null, accountNameAvailable);
        });

    });
}