Ordering posts in Search & taxonomy by post_meta

Question

I'm not sure if im going about this the right way or not, seems to be alot of people doing this, but with completely different ways of doing it from queries in templates to functions so im not sure which route to go down.

I have a custom post type (business) which has featured posts, Each of these posts have a "featured_listing" post_meta which is either EMPTY or "featured-listing" value** attached to the post. I'd like to display the posts which do not have an empty post_meta value above all other posts in search results and categories.

**Note the - rather than _ for the value.

This is what I thought might work, but I'm starting to think I'm barking up the wrong tree.

// Order posts by meta data
function custom_special_sort( $query ) {
    //is this the main query and is this post type of post
    if ( $query->is_main_query() && $query->is_post_type( 'business' ) ) {
        //Do a meta query
        $query->get_post_meta(get_the_ID(), "featured_listing", TRUE);

        //sort by a meta value
        $query->set( 'orderby', 'featured_listing' );
        $query->set( 'order', 'ASC' );
    }
}
add_action( 'pre_get_posts', 'custom_special_sort' );

I've also just tried to do it slightly differently, below. But could do with some guidance as to why its not working or if im even doing it correctly:

    function custom_special_sort( $query ) {
    // Check this is main query and other conditionals as needed
    if ( $query->is_main_query() && $query->is_post_type( 'business' ) ) {
        $query->set( 
          'meta_query', 
          array( 
            array(
              'key' => 'featured_listing',
              'value' => 'featured-listing',
              'orderby' => 'featured_listing',
              'order' => 'DESC'  
            )
          )
        );
    }
  }
add_action( 'pre_get_posts' , 'custom_special_sort' );

Answer 1

You have a couple of issues with the code you are trying.

To check the query is for your CPT archive: You are using $query->is_post_type() but it doesn't work (as far as I know, its not even a function). Instead you can use either:

if (is_post_type_archive('business')) {...}

or (if its not only on the archive page)

if ($query->get('post_type') == 'business') {...}

To order by meta value in pre_get_posts, you need to set the meta_key as well as the orderby (and optionally order).

Complete Function: Applying these to your "custom_special_sort" function, we get:

function custom_special_sort( $query ) {

    // if is this the main query and is this post type of business
    if ( $query->is_main_query() && is_post_type_archive( 'business' ) ) {

        // order results by the meta_key 'featured_listing'
        $query->set( 'meta_key', 'featured_listing' );
        $query->set( 'orderby', 'featured_listing' );
        $query->set( 'order', 'DESC' );
    }
}
add_action( 'pre_get_posts', 'custom_special_sort' );

Answer 2

I have marked Fluffykittens answer above as the correct answer. I wanted to extend the answer ( Hopefully it will help someone else ).

With the answer provided by Fluffykitten I found that with my particular theme, I'm using different loop for archives and custom taxonomy which resulted in the re-ordering of posts working on my search archives where is_post_type_archive was true. However my taxonomy archives the reordering wasnt happening, so changing the query to include is_tax made it work.

Not sure if its the best way of adding to the query as im a php novice, but it works. Someone is welcome to correct/improve :)

function custom_special_sort( $query ) {

    // if is this the main query and is this post type of business

    if ( ($query->is_main_query() && is_post_type_archive('business')) || (is_main_query() && is_tax ('location')) ) {

        // order results by the meta_key 'featured_listing'
       $query->set( 'meta_key', 'featured_listing' );
        $query->set( 'orderby', 'featured_listing' );
        $query->set( 'order', 'DESC' );
    }
}
add_action( 'pre_get_posts', 'custom_special_sort' );