protected function insert(array $data = array())
    {
        $fields = array();
        $values = array();
        
        foreach ($data as $field => $value) {
            $fields[] = $field;
            $values[] = '?';
        }
        
        $sql = "INSERT INTO $this->_table " 
                . "(" . implode(', ', $fields) . ")"
                . "VALUES (" . implode(', ', $values) . ")";
                
        $pdos = $this->_pdo->prepare($sql);
        
        $pdos->execute(array_values($data));
        
        return $pdos->statement()->rowCount();
    }