How can i order by existence of thumbnail in Wordpress?

php, thumbnails, wordpress

Solution

This is an interesting issue. WordPress currently doesn't have a method to get all the posts with thumbnails and without thumbnails in one query with their inbuilt `WP_Query` method. But we can do a hack for that, probably not the best I think but will work :)

Add this function in your themes functions.php file

function remove_metakey ($where) {

    global $wpdb;

    $where = str_replace("AND (".$wpdb->postmeta.".meta_key = '_thumbnail_id' )", "", $where);

    return $where;
}

Add this filter just before you call `new WP_Query` Object

add_filter ('posts_where_request', 'remove_metakey');

So the full thing will look like:

add_filter ('posts_where_request', 'remove_metakey');

$the_query = new WP_Query(array(
               'post_type' => 'veiculos',
               'posts_per_page'=> -1,
               'meta_key' => '_thumbnail_id',
               'orderby' => 'meta_value_num',
               'order' => 'DESC',
               'tax_query' => array(
                 array(
                   'taxonomy' => 'categoria-veiculo',
                   'field' => 'id',
                   'terms' => 5
                 )
               )
           ));

You have to add the filter before you call the WP_QUery object else it will not work. Also don't add this filter in your functions.php file because then it will be rendered when ever `posts_where_request` is made.

What this does is that when we are executing the query with `WP_Query` object, it calls the `posts_where_request`. We are hooking our own function with `posts_where_request`. So when `posts_where_request` is called our function will be rendered. In our function we are using `str_replace` to replace the meta_key part in the `$where` value and returning it. This will remove the meta_key condition in where part in the query.

UPDATE :

I have found the correct method to remove the meta key from where condition using WordPress hook. This is much better and cleaner way to do :

Add this hook before you call the WP_Query object. Instead of the earlier hook use this.

add_filter ('get_meta_sql', 'remove_metakey');

Now replace the earlier function with this :

function remove_metakey ($array) {

    $array['where'] = ''; //you can also use unset, but setting the value to null is better to avoid warnings

    return $array;
}

The complete thing will be :

add_filter ('get_meta_sql', 'remove_metakey');

$the_query = new WP_Query(array(
               'post_type' => 'veiculos',
               'posts_per_page'=> -1,
               'meta_key' => '_thumbnail_id',
               'orderby' => 'meta_value_num',
               'order' => 'DESC',
               'tax_query' => array(
                 array(
                   'taxonomy' => 'categoria-veiculo',
                   'field' => 'id',
                   'terms' => 5
                 )
               )
           ));

This is the correct way to do it. It sets the `where` value to `null` thus preventing an additional meta key condition in the SQL query.

Remember add this filter only when you need. Also don't add this in functions.php, then it will be executed each time the get_meta_sql function is called.

Hope this helps you :)

Problem

Original source