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/**
     * Sets carriers assigned to the product.
     *
     * @param int[] $carrier_list
     */
    public function setCarriers($carrier_list)
    {
        $data = [];

        foreach ($carrier_list as $carrier) {
            $data[] = [
                'id_product' => (int) $this->id,
                'id_carrier_reference' => (int) $carrier,
                'id_shop' => (int) $this->id_shop,
            ];
        }
        Db::getInstance()->execute(
            'DELETE FROM `' . _DB_PREFIX_ . 'product_carrier`
            WHERE id_product = ' . (int) $this->id . '
            AND id_shop = ' . (int) $this->id_shop
        );

        $unique_array = [];
        foreach ($data as $sub_array) {
            if (!in_array($sub_array, $unique_array)) {
                $unique_array[] = $sub_array;
            }
        }

        if (count($unique_array)) {
            Db::getInstance()->insert('product_carrier', $unique_array, false, true, Db::INSERT_IGNORE);
        }
    }

This is a function from Product.php

Db::INSERT_IGNORE does not write a duplicate record to the database on an index collision. You wrote that you were trying to somehow add records to the database. Incorrect recording may have occurred and this causes a problem with saving new records.