lithium\data\collection\DocumentArray::__isset PHP Method

$document->_id.

public __isset ( $name ) : boolean
$name		The field name, as specified with an object property.
return	boolean	Returns `true` if the field specified in `$name` exists, otherwise `false`.

    public function __isset($name)
    {
        return isset($this->_data[$name]);
    }

DocumentArray