Prestashop : use Product class in personnal script - php

Question

I need to create a cron script to process products (add, delete, update) when I get them from a raw data file from a third party firm which sends a new file (data separated with ;) whenever a product is changed (added, deleted, updated).
I tried using the Product class (from Product.php) to add new products in the shop. The problem at first was that I got this error :
class 'ObjectModel' not found in importProducts.php
I found an apparent solution, which was to require_once the config and init file from the config folder in importProduct.php :
require_once(dirname(__FILE__).'/../config/config.inc.php');
require_once(dirname(__FILE__) . '/../init.php');
The require points to the right files. My file is located in a new folder, called "crontasks".
prestashop/crontaskt/import.php
(import.php starts importProduct.php)
But now there is a new error :
Fatal error: Uncaught 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 '' at line 7
SELECT c.id_category
FROM ps_category_product cp
LEFT JOIN ps_category c ON (c.id_category = cp.id_category)
INNER JOIN ps_category_shop category_shop ON (category_shop.id_category = c.id_category AND category_shop.id_shop = 1)
WHERE cp.id_category NOT IN (18)
AND cp.id_product = thrown in D:\Travail\BUSCI\prestashop\prestashop\classes\db\Db.php on line 791
(they don't appear, but around the query are < br />< br />< pre >...< /pre > without the spaces in it)
Problem is, I checked in the database, and the columns are all there, and I don't get why there is a problem on that line.
Also, I could not find from which file that query was. I looked in Product.php, and I found one very similar but not exactly the same :
$result = Db::getInstance()->executeS('
SELECT c.`id_category`
FROM `'._DB_PREFIX_.'category_product` cp
LEFT JOIN `'._DB_PREFIX_.'category` c ON (c.`id_category` = cp.`id_category`)
'.Shop::addSqlAssociation('category', 'c', true, null, true).'
WHERE cp.`id_category` NOT IN ('.implode(',', array_map('intval', $categories)).')
AND cp.id_product = '.$this->id
);
line 1051 in Product.php, method updateCategories.
I could not find anything similar in Category.php or any other file I looked in. But this query is missing the inner join, so I don't know if that's really the one. I suppose the problem comes from the fact that there is nothing after the =, but I don't know if that's just a character limitation (amount of characters printed in an error) or if it is the error. I'm feeling a little lost.
I did not change any files from prestashop. This is the latest update I just installed a week ago on my computer. The tests are done in local, on my computer.
I would really appreciate some help.
Excuse me for my english, it's not amazing.
Edit :
So I searched through the whole project, in every file for the line
INNER JOIN '._DB_PREFIX_.'category_shop
and could not find it. I tried taking away the extra spaces, just in case, but could not find the file in which this sql query is in.