public static function _isPurchasable($a_ref_id, $a_vendor_id = 0, $a_check_trustee = false, $a_check_status = false)
 {
     global $ilDB;
     // In the moment it's not possible to sell one object twice
     $data = array();
     $data_types = array();
     $query = 'SELECT * FROM payment_objects WHERE ref_id = %s ';
     $data_types[] = 'integer';
     $data[] = $a_ref_id;
     // check if object is buyable !!
     if ($a_check_status) {
         $query .= 'AND status > %s ';
         $data_types[] = 'integer';
         $data[] = 0;
     }
     if ($a_vendor_id > 0) {
         $query .= 'AND vendor_id = %s';
         $data_types[] = 'integer';
         $data[] = $a_vendor_id;
         if ($a_check_trustee) {
             include_once './Services/Payment/classes/class.ilPaymentTrustees.php';
             include_once './Services/Payment/classes/class.ilPaymentVendors.php';
             $vendors = ilPaymentTrustees::_getVendorsForObjects($a_vendor_id);
             if (ilPaymentVendors::_isVendor($a_user_id)) {
                 $vendors[] = $a_user_id;
             }
             if (is_array($vendors) && count($vendors)) {
                 $query .= ' OR ' . $ilDB->in('vendor_id', $vendors, false, 'integer');
             }
         }
     }
     $res = $ilDB->queryf($query, $data_types, $data);
     $rows = $ilDB->numRows($res);
     return $rows ? true : false;
 }
 private function __getVendors()
 {
     include_once 'Services/Payment/classes/class.ilPaymentVendors.php';
     $options = array();
     $vendors = array();
     if (ilPaymentVendors::_isVendor($this->user_obj->getId())) {
         $vendors[] = $this->user_obj->getId();
     }
     if ($vend = ilPaymentTrustees::_getVendorsForObjects($this->user_obj->getId())) {
         $vendors = array_merge($vendors, $vend);
     }
     foreach ($vendors as $vendor) {
         /** @var $tmp_obj ilObjUser */
         $tmp_obj = ilObjectFactory::getInstanceByObjId($vendor, false);
         $options[$vendor] = $tmp_obj->getFullname() . ' [' . $tmp_obj->getLogin() . ']';
     }
     return $options;
 }