How to Order Posts by Taxonomy in WordPress?

To order posts in WordPress based on a taxonomy term, you’ll need to use the WP_Query class with some customization. WordPress doesn’t support ordering results directly by taxonomy terms out of the box, so you’ll typically need to employ a workaround. Here’s a general approach using WP_Query and custom SQL clauses to order posts by a specific taxonomy term:

Basic Approach:

Identify the Taxonomy: First, determine the taxonomy you want to order your posts by (e.g., category, post_tag, or a custom taxonomy like product_cat).
Custom Query with WP_Query: Use WP_Query to fetch the posts, and then apply custom order logic. Since direct ordering by taxonomy term is not natively supported, you might need to first retrieve the terms in the order you want, and then loop through these terms to fetch and display posts.

Advanced Custom Ordering:

For a more direct approach that involves ordering by taxonomy terms in a single query, you can use the posts_clauses filter to modify the SQL query that WP_Query generates. This requires a good understanding of SQL and WordPress’s database structure.

Here is an example of how you might implement this:

add_filter('posts_clauses', 'order_posts_by_taxonomy_term', 10, 2);

function order_posts_by_taxonomy_term($clauses, $wp_query) {
    global $wpdb;

    // Only modify the query if our custom flag is set
    if ($wp_query->get('orderby_taxonomy')) {

        // The taxonomy we're ordering by
        $taxonomy = $wp_query->get('orderby_taxonomy');

        // Modify the join to include the taxonomy relationship
        $clauses['join'] .= "
            LEFT OUTER JOIN {$wpdb->term_relationships} ON {$wpdb->posts}.ID={$wpdb->term_relationships}.object_id
            LEFT OUTER JOIN {$wpdb->term_taxonomy} ON {$wpdb->term_relationships}.term_taxonomy_id={$wpdb->term_taxonomy}.term_taxonomy_id
            LEFT OUTER JOIN {$wpdb->terms} ON {$wpdb->terms}.term_id={$wpdb->term_taxonomy}.term_id
        ";

        // Modify the where clause to filter by our taxonomy
        $clauses['where'] .= $wpdb->prepare(" AND ({$wpdb->term_taxonomy}.taxonomy = %s)", $taxonomy);

        // Modify the order clause to order by term name
        $clauses['orderby'] = "{$wpdb->terms}.name ASC";
    }

    return $clauses;
}

// Use the modified query
$query = new WP_Query(array(
    'post_type' => 'post', // or your custom post type
    'orderby_taxonomy' => 'your_taxonomy', // custom flag to trigger our filter
));

add_filter('posts_clauses', 'order_posts_by_taxonomy_term', 10, 2);

function order_posts_by_taxonomy_term($clauses, $wp_query) {

global $wpdb;

// Only modify the query if our custom flag is set

if ($wp_query->get('orderby_taxonomy')) {

// The taxonomy we're ordering by

$taxonomy = $wp_query->get('orderby_taxonomy');

// Modify the join to include the taxonomy relationship

$clauses['join'] .= "

LEFT OUTER JOIN {$wpdb->term_relationships} ON {$wpdb->posts}.ID={$wpdb->term_relationships}.object_id

LEFT OUTER JOIN {$wpdb->term_taxonomy} ON {$wpdb->term_relationships}.term_taxonomy_id={$wpdb->term_taxonomy}.term_taxonomy_id

LEFT OUTER JOIN {$wpdb->terms} ON {$wpdb->terms}.term_id={$wpdb->term_taxonomy}.term_id

// Modify the where clause to filter by our taxonomy

$clauses['where'] .= $wpdb->prepare(" AND ({$wpdb->term_taxonomy}.taxonomy = %s)", $taxonomy);

// Modify the order clause to order by term name

$clauses['orderby'] = "{$wpdb->terms}.name ASC";

}

return $clauses;

}

// Use the modified query

$query = new WP_Query(array(

'post_type' => 'post', // or your custom post type

'orderby_taxonomy' => 'your_taxonomy', // custom flag to trigger our filter

));

This code adds a custom filter to modify the SQL query executed by WP_Query. It joins the necessary tables to include taxonomy terms in the query and then orders the results by the term name. Remember to replace 'your_taxonomy' with the actual taxonomy you want to order by.

Important Considerations:

Performance: This approach can impact database performance, especially for large datasets. Test thoroughly.
Maintenance: Directly modifying SQL queries can lead to maintenance issues with WordPress updates. Keep your modifications documented and review them after updates.

This approach requires careful implementation and testing. If you’re not comfortable writing SQL or PHP, consider seeking help from a developer familiar with WordPress development.