public function getField($field_name)
    {
        $field = null;
        
        if (isset($this->m_fields[$field_name]))
        {
            $field = $this->m_fields[$field_name];
        }
        else
        {
            $err_msg = '[' . $field_name . '] does not exist in table ' .
                       '[' . $this->m_name . ']';
            
            throw new \Exception($err_msg);
        }
        
        return $field;
    }