relevanssi_missing_sort_key

apply_filters( 'relevanssi_missing_sort_key', string $key_value, string $key_name );

Fills in the missing sort key in case a custom field sorting has a missing key.

Parameters

$key_value
(string) The sorting field value.

$key_name
(string) The name of the custom field.

More information

In some cases the sorting method may not have values for all posts (for example when sorting by menu_order). If you still want to use a sorting method like this, you can use this function to fill in a default value.

A good default value for numeric fields sorted in ascending order (like menu_order) is PHP_INT_MAX, which is the largest possible number. When sorting in descending order, a decent default value is 0.

add_filter( 'relevanssi_missing_sort_key', 'rlv_default_key', 10, 2 );
/**
 * Add default values.
 *
 * @param string $value The sorting field value.
 * @param string $key   The sorting field name.
 *
 * @return string The sorting field value.
 */
function rlv_default_key( $value, $key ) {
    if ( 'menu_order' === $key ) {
        $value = PHP_INT_MAX;
    }
    return $value;
}