public function __call($method, $params)
{
$method = strtoupper($method);
if ($method != 'AND' && $method != 'OR') {
throw new \BadMethodCallException("Unknown method {$method}");
}
if (!empty($this->_sql)) {
$this->_sql = "({$this->_sql}) {$method} ";
}
$this->_sql .= implode(" {$method} ", $params);
return $this;
}