TypeError：无法将未定义或空值转换为对象 - 尝试在路由器中执行 MySQL 查询时

Posted 2023-02-22

【中文标题】TypeError：无法将未定义或空值转换为对象 - 尝试在路由器中执行 MySQL 查询时

【英文标题】：TypeError: Cannot convert undefined or null to object - when trying to execute MySQL query in router

【发布时间】：2022-01-21 12:40:41

【问题描述】：

我有一个执行几个 mysql 查询的路由 - 最终查询是一个 SELECT，它使用路由中执行的前一个查询中的“电子邮件”值作为条件。我已经使用 MySQL Workbench 测试了其中一些“电子邮件”值并得到了结果，所以我很确定我的 JS 代码是错误的。不确定这是否需要采用异步/等待方法，但感觉可能是这样 - 我只是不确定从哪里开始。

这是错误：

以及抛出错误的行（330）：

这是路线的完整代码：

// ROUND III: GETTING EVENTS AND ENROLLMENTS BY EMAIL FROM eLearningRecords TABLE; Then will need to create a SELECT query joining enrollmentrefresh and tb_elr_prereqs on emial. 
// All learndot enrollments GET route .......................................................................................................
// .................................................................................................................................
router.get("/elearning_enrollments", (err, res) => 
    // STEP 3 - DELETE EXISTING DATA FROM THE tb_elr_prereqs table ===========================================================
    // create the DELETE query and set to variable
    var sql_delete_events_and_enrollments = `DELETE FROM tb_elr_prereqs;`

    // execute the DELETE query
    pool2.query(sql_delete_events_and_enrollments, (err, results, fields) => 
        if (err) 
            console.log("Failed to delete records from tb_elr_prereqs!!!")
            console.log(err)
            res.sendStatus(500)
            return
        
        console.log("Deleted the existing data from the tb_elr_prereqs table");
        // res.end()
    
    // END (STEP 3) DELETE QUERY SECTION ===========================================================================================

    // =============================================================================================================================

    // STEP 4 - GET EVENTS AND ENROLLMENTS FROM contact, enrollment, and location tables ===========================================

    // create a function
    function get_elearningrecords()
    var sql_getemails = `SELECT email FROM enrollmentrefresh;`
    
    // execute the query
    pool.query(sql_getemails, (err, rows, results)=>
        console.log("getting the emails from enrollmentrefresh table")
        console.log("sql_getemails" + Object.keys(rows).length)
        for(i=1;i <= Object.keys(rows).length; i++)
            if(rows[i] != undefined)
                for(var i in rows)
                    var email = JSON.stringify(rows[i].email)
                    var email = email.replace('"\\"', '')
                    var email = email.replace('\\""', '')
                    console.log(email)
                    var sql_getelr = 
                        `SELECT
                            registrationID,
                            courseName,
                            email
                        FROM
                            eLearningRecords
                        WHERE
                            email = "$email"
                        (
                            SCORMLESSONSTATUS LIKE 'passed'
                            OR 
                            registrationstatus LIKE 'PASSED'
                        )
                        AND
                        (
                            (courseName LIKE '%Fundamentals%' AND courseName LIKE '%Part 3%')
                            OR 
                            courseName LIKE '%Creating Dashboards%'
                            OR 
                            courseName LIKE '%Advanced Searching%'
                            OR 
                            courseName LIKE '%Core Consultant Labs%'
                        );`

                    console.log(sql_getelr);
                    // execute the SELECT query
                    pool2.query(sql_getelr, (err, rows, results)=>
                        console.log("sql_getelr" + Object.keys(rows).length)
                    )
                
            
        
    )


    get_elearningrecords();

    )
)

【参考方案1】：

你的基本问题在于这里有问题

WHERE
        email = "$email"
    (
        SCORMLESSONSTATUS LIKE 'passed'
        OR 
        registrationstatus LIKE 'PASSED'
    )

这不是有效的 sql 代码。

这应该是

WHERE
  email = "$email"
AND
    (
        SCORMLESSONSTATUS LIKE 'passed'
        OR 
        registrationstatus LIKE 'PASSED'
    )

还有

$email

这看起来更像是 php 代码而不是 javascript

看看Preventing SQL injection in Node.js如何在javascript中传递数据

【参考方案2】：

问题出在第 294 行。来自数据库的响应总是以数组的形式出现（rows）。

您正在尝试在引发错误Cannot convert undefined or null to object 的数组上使用 Object 方法。你应该在数组上使用数组方法。

将以下几行更改为：

第 294 行：console.log("sql_getemails" + rows.length)

第 295 行：for(i=1;i <= rows.length; i++)

第 297 行：rows.forEach(i=> //your code goes here)

其余的看起来不错，但不是很好。您的代码正在陷入回调地狱。为了避免回调地狱，我建议在你的函数和路由上使用async/await。