为什么此代码会发送重复的电子邮件？

Question

我们在 Azure 上运行一个调度程序，它每分钟运行一次，并检查数据库以查看需要为我们的应用发送哪些电子邮件并发送它们。

这在绝大多数情况下都有效，但有时，在几个小时内，调度程序会开始重复发送大多数电子邮件（最多 5 份）。

    query = "select id, email, textbody, htmlbody, subject from emailTable where sent = 0 AND DateSent IS NULL";
mssql.query(query, {
    success: function(results) {
        for(var i = 0 ; i < results.length; i++)
        {
            handleItem(results[i]);
        }
    },
    error: function(err) {
        console.log("Error : " + err);
    }
});

function handleItem(item) {
        sendMail(item); 
        var query = "update emailTable SET sent = 1, DateSent = GETDATE() where id = ?";
        mssql.query(query, [item.id]);

}

function sendMail(objMail)
{
    sendgrid.send({
      to:       objMail.email,
      from:     'source@sourcemail.com',
      fromname: "Source",
      subject:  objMail.subject,
      text:     objMail.textbody,
      html:     objMail.htmlbody
    }, function(err, json) {
      if (err) { return console.error(err); }
    });
}

当它开始失败时，就好像 handleItem 或 sendMail 为同一个项目被多次调用。循环或解释这种行为的一般逻辑有什么问题吗？

Answer 1

Try writing the update query in the callback function for sendMail(item)

eg. sendMail(item,function(){
 var query = "update emailTable SET sent = 1, DateSent = GETDATE() where id = ?";
        mssql.query(query, [item.id]);
});

function sendMail(objMail,cb)
{
    sendgrid.send({
      to:       objMail.email,
      from:     'source@sourcemail.com',
      fromname: "Source",
      subject:  objMail.subject,
      text:     objMail.textbody,
      html:     objMail.htmlbody
    }, function(err, json) {
      if (err) { cb(err) }
       cb(null,json)
    });
}