martin_666 on "WP_Query - multiple custom post types and sort by custom meta"

Hello guys,

I'd like get results from two custom post types and sort them by custom meta (date of start events).

This code:

$warsztaty_q = new WP_Query(array(
	'post_type' => array('kalendarium', 'warsztaty'),
	'order_by' => 'meta_value',
	'meta_key' => 'data_start',
	'order' => 'ASC'
));

Would be ok but first sorted is 'kalendarium' and then 'warsztaty' so in query results first sorted are posts from 'kalendarium' and next from 'warsztaty' not together.

I found this solution:
http://wordpress.stackexchange.com/questions/71576/combining-queries-with-different-arguments-per-post-type

But I can't get custom meta :(

Anyone can help me? :)