Can't sort order of wp_query with 2 meta keys

Question

I'm trying to display custom post types by excluding the sold ones but also by displaying them in alphabetical order from the county meta_key.

I'm trying to use pre_get_posts but I'm not sure that I doing it correctly

Here is my code on a page template:

$args = array(
    'post_type'      => 'property',
    'orderby'        => 'meta_value',
    'meta_key'       => 'random_775',
    'order'          => 'ASC',
    'posts_per_page' => 100,
); 

$view_all_properties_sorted = new WP_Query( $args ); 

and here is the function in my functions.php file:

 add_action( 'pre_get_posts', 'sort_view_all_properties' );
 function sort_view_all_properties($view_all_properties_sorted) { 
    $view_all_properties_sorted->set('meta_key', 'sold');
    $view_all_properties_sorted->set('meta_value', 'true');
    $view_all_properties_sorted->set('meta_compare', '!=');
 }

When I use this code, I'm getting a 404 error when I add this line:

$view_all_properties_sorted->set('meta_key', 'sold');

Is it because meta_key has already been set? Any suggestions on what I may be doing wrong?

Answer 1

As you can read in Codex about orderby and the WP_Query, you can use multiple orderby values as well:

'orderby' => 'name meta_value'

simply by using a space in between. The available orderby values are listed in the Codex page.

About your question: By default it should already work with your query. If it doesn't, you'll have to add the output from posts_clauses, posts_request or use the pre_get_posts filter. More details in this answer.