Node.js MySQL query error ER_PARSE_ERROR - mysql

Question

I have a problem with a MySQL query inside of a NodeJS application. In my snippet I loop through a triple-nested for cycle and save some different data in the post variable. What I want to do is checking whether this data already exists into the database and, if not, execute an INSERT query.
Been trying in any possible way, however I get the following error:
Error: ER_PARSE_ERROR: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ' `user_id` = '421', `product_id` = '1', `brick_id` = '1', `effect_date` = '2016-' at line 1
I don't think there are any SQL errors, I have been checking a thousand of times but maybe I am missing something. This is what I tried to do:
router.post('/relations/finalize', function (req, res, next) {
// Executing a cycle for every possible data combination
for (var i = 0; i < req.body.users_selection.length; i++) {
for (var j = 0; j < req.body.products_selection.length; j++) {
for (var k = 0; k < req.body.bricks_selection.length; k++) {
post = {
owner_id: req.session.userid,
user_id: req.body.users_selection[i],
product_id: req.body.products_selection[j],
brick_id: req.body.bricks_selection[k],
effect_date: req.body.year + "-" + req.body.month + "-01 00:00:00",
}
// Checking if the entry already exists
req.app.locals.connection.query({
sql: 'SELECT * FROM relations WHERE user_id = ? AND product_id = ? AND brick_id = ? AND effect_date >= ?',
timeout: 40000, // 40s
values: [post]
}, function (err, rows, fields) {
if (err) throw err;
else {
if (rows.length > 0) {
console.log("The entry already esists");
} else {
req.app.locals.connection.query("INSERT INTO relations SET ?", post, function (err, row, fields) {
if (err) throw err;
else {
console.log("The entry didn't exists and was then created.");
//res.redirect("/relations/wizard");
}
});
}
}
});
}
}
}
});
Any help will be greatly appreciated to solve this issue.
EDIT: I also tried to pass separate values into the SELECT query, like this:
values: req.body.users_selection[i], req.body.products_selection[j], req.body.bricks_selection[k], req.body.year + "-" + req.body.month + "-01 00:00:00"
But the result I get is that the INSERT query is called X times with the same values, as the for loops are not going through, maybe because of the asynchronous nature of Node..