WordPress WP_Query with & operator in meta_query not working. How to combine queries?

I am trying to show some posts on a front page grid. For that I need to combine 2 queries. I want to show

a) all posts with 'post_type' => 'project'

AND

b) all posts with 'post_type' => 'post', which are 'category__not_in' => array(1,4,5,6,8), and which have the meta_key 'show_in_grid' set to 1

They are displayed with random sorting all in one list.

In the WordPress documentation for WP_Query it says you can do for example:

$query = new WP_Query( 'meta_value=blue&post_type=page' );

but this doesn’t seem to work as expected.

If i do:

'post_type=post&meta_key=show_in_grid&meta_value=1'

it just ignores whether or not the key is set to 1 or not.

If i do:

'post_type' => 'post',
'meta_query' => array(
             array( 'key' => 'show_in_grid',              
                  'value' => '1',
                'compare' => '=')),

then, everything works as expected.

Is this an error in the Documentation? And how can I have 2 different queries combined with a logical OR? I saw there is something like that for tax_query using ‘relation’.

Answer

Ok, i got it to work thanks to the comments here: http://wordpress.org/support/topic/multiple-queries-compiling-into-one-loop?replies=5#post-1929074

The final solution is this:

<?php
            // first query
            $blogposts = get_posts(array(
                    'category' => 5,
                    'post_type' => 'post',
                    'meta_query' => array(
                            array('key' => 'show_in_grid',
                                'value' => '1',
                                'compare' => '=')),
                    'post_status' => 'publish',
                    'posts_per_page' => 1000
                    ));
            // second query
            $projects = get_posts(array(
                    'post_type' => 'project',
                    'post_status' => 'publish',
                    'posts_per_page' => 1000
                    ));

            $mergedposts = array_merge( $blogposts, $projects ); //combine queries

            $postids = array();
            foreach( $mergedposts as $item ) {
            $postids[]=$item->ID; //create a new query only of the post ids
            }

            $uniqueposts = array_unique($postids); //remove duplicate post ids

            $args = array(
                    'post_type' => array('project','post'),
                    'post__in' => $uniqueposts,
                    'orderby' => 'rand'
                    );

            $loop = new WP_Query($args);

            while ( $loop->have_posts() ) : $loop->the_post();?>

For some strange reason ‘post_type’ had to be specified in the original 2 queries AND the final query otherwise it wouldn’t work !?

Hope this helps someone.. 🙂