code: protected function getValuesList($dataMember, $offset)
       {
           if(is_array($this->{$dataMember}[$offset])) {
               $items = $this->{$dataMember}[$offset];
               $count = count($items);
               $result = ' (';
               for($i=0; $i<$count; $i++) {
  
                   if ($items[$i] == 'NULL') {
                       $result .= $items[$i];
                   }
                   else {
                       $result .= "'".$this->clean($items[$i])."'";
                   }
  
                   if ($count-1 != $i) {
                       $result .= ', ';
                   }
               }
               $result .= ')';
               return $result;
           }
           else {
               if ($this->{$dataMember}[$offset] == 'NULL') {
                   return $this->{$dataMember}[$offset];
               }
               else {
                   return "'".$this->clean($this->{$dataMember}[$offset])."'";
               }
           }
       }
docs: Returns a string for the VALUES (value1, value2, value3), (value1, value2, value3), ...
  part of an INSERT statement.