Efficiently sort only certain categories by custom field

Question

I have a site with about 1,000 posts spread out over 70 or 80 categories. Some of these categories require the posts be sorted by a custom field, others not.

I've got a working solution by having 60+ category template files defined (e.g. category-123.php, category-124.php) and each of those calls a separate loop file:

get_template_part( 'loop-123', 'category' );

The loop-123 file then runs a new query and sorts it correctly before passing it to the loop:

<?php
$the_query = new WP_Query("cat=123&meta_key=programnumber&orderby=meta_value&order=ASC");
?>
<?php while ( $the_query->have_posts() ) : $the_query->the_post(); ?>

However, there has to be a more efficient way to do this than to create 60+ file pairs. I'm just not seeing it, though.

Answer 1

I would suggest to hook onto pre_get_posts and alter the query, rather than firing off your own in the template (it keeps your template tidy, and you'll avoid doubling your database queries!).

Below demonstrates this, plus a bonus settings field in the admin (under "Reading") to select the categories that "special sorting" applies to - see how easy the settings API really is!

/**
 * Intercept the query & attach our own parameters if the conditions are met.
 */
function wpse_42457_custom_category_order( $wp_query )
{
    if ( ! $wp_query->is_category() ) // save proceeding processing
        return;

    $special_categories = wp_parse_id_list( get_option( 'sorted_categories' ) );
    if ( $wp_query->is_category( $special_categories ) ) {

        // We've got a winner - set our special params.
        $wp_query->set( 'meta_key', 'programnumber' );
        $wp_query->set( 'orderby', 'meta_value' );
        $wp_query->set( 'order', 'ASC' );
    }
}
add_action( 'pre_get_posts', 'wpse_42457_custom_category_order' );

/**
 * Register the sorted categories option & the settings field.
 */
function wpse_42457_admin_init()
{
    add_settings_field( 'sorted_categories', 'Special Categories', 'wpse_42457_setting_field', 'reading', 'default' );
    register_setting( 'reading', 'sorted_categories', 'wpse_42457_setting_sanitize' );
}
add_action( 'admin_init', 'wpse_42457_admin_init' );

/**
 * Sanitize our checked categories by turning back to a comma-delimited string.
 *
 * This'll save bytes in the options table, plus it can be "unserialized" more
 * efficiently with wp_parse_id_list() when it's actually needed.
 */
function wpse_42457_setting_sanitize()
{
    // wp_terms_checklist uses "post_category" POST name.
    if ( isset( $_POST['post_category'] ) )
        $value = $_POST['post_category'];
    else
        $value = array(); // none checked

    return implode( ',', wp_parse_id_list( $value ) );
}

/**
 * Display the sorted categories field.
 */
function wpse_42457_setting_field()
{
    // Please forgive me for this dirty HTML!
    ?>

<style>#sorted_categories li li { margin: 0 0 0 15px }</style>
<ul id="sorted_categories">
    <?php
        wp_terms_checklist( 0, array(
            'selected_cats' => wp_parse_id_list( get_option( 'sorted_categories' ) ),
            'checked_ontop' => false,
            'taxonomy' => 'category'
        ));
    ?>
</ul>

    <?php
}

Whilst I always feel like I should encourage others to take steps for themselves, this proved easier to code up than walk through - hopefully it'll be educational nontheless!

---

You'll need to drop this in a custom plugin, or your theme's functions.php.

Answer 2

How about this, create an option in the options table (in the database) with an array of categories ids that need a custom sorting ex:

<?php
$cats_to_sort = array(21,33,43,66); //add as many as you need.
update_option('cats_to_sort',$cats_to_sort);
?>

then creat a single category.php file with a simple loop but before the loop check if this category needs to be sorted by a custom field ex:

<?php
//get the saved array
$cats_to_sort = get_option('cats_to_sort');
//get the category id, this works for custom taxonomies as well.
$term_slug = get_query_var( 'term' );
$taxonomyName = get_query_var( 'taxonomy' );
$term = get_term_by( 'slug', $term_slug, $taxonomyName );
if (in_array($term->term_id,$cats_to_sort)){
    query_posts("cat=".$term->term_id."&meta_key=programnumber&orderby=meta_value&order=ASC");
}
//you loop here
?>