How to combine meta_query and post__in in WP_Query

Question

I have built a complex query which should do 3 things:

1. select posts with ids in the $additional_ids array using post__in;
2. ignore posts with ids in the $ignore_ids array using post__not_in;
3. select posts with a combination of cpt values (ie. is an animal, is blue and eats grass) using meta_query.

Here's what I have so far:

$args_assets = array(
        'post_type' => 'assets',
        'posts_per_page' => -1,
        'post__in' => $additional_ids,
        'post__not_in' => $ignore_ids,
        'meta_query' => array(
            'relation' => 'AND',
            $query_animal,
            $query_color,
            $query_food,
        ),
        'orderby' => 'title',
        'order' => 'asc',
        );

The query works fine WTHOUT the 'post__in' => $additional_ids line. As soon as I add the post__in argument, the query returns an empty result.

Is it possible to combine post__in with a meta_query? If so, what's the best method?

Thanks in advance for any help!

Answer 1

post__in and post__not_in are mutually exclusive.

Note: you cannot combine post__in and post__not_in in the same query.

http://codex.wordpress.org/Class_Reference/WP_Query

Either make the query with post__in and meta_query combination or make the query with post__not_in and meta_query combination. Any of them but not the union of them.