Why is this code sending duplicate emails? - node.js

Question

We're running a scheduler on Azure that runs every minute and checks in a database to see what emails need to be sent for our app and sends them.
This works the vast majority of the time but once in a while, for a few hours, the scheduler starts sending most emails in duplicates (up to 5 copies).
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); }
});
}
When it starts failing it's as if handleItem or sendMail is called multiple times for the same item. Is there anything wrong with the loop or the general logic that would explain this behavior ?

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)
});
}