Sort WordPress Terms with term_meta Custom Fields

In an earlier article, I recommended the WordPress sorting plugin Anything Order. It is convenient, but in some situations it can conflict with other plugins. Before WordPress 4.4, taxonomy term ordering was limited to built-in fields such as id, term_id, name, and slug. WordPress 4.4 introduced support for taxonomy custom fields through term_meta, and that gives us a clean way to sort terms using our own custom numeric value.

Add an input field for the term’s custom sort value

First, we need to add a custom field to the taxonomy term edit form. After doing that, a sort-order field appears when we edit the category in the dashboard. We can enter numbers from small to large according to the sorting order we want.

/**
 * Taxonomy term order field
 *
 * @param        Term Object $term
 * @param string $taxonomy
 */
add_action( 'category_edit_form_fields', 'term_order_field', 10, 2 );
function term_order_field( $term, $taxonomy ) {
   ?>

   <table class="form-table">
      <tbody>
      <tr class="form-field">
         <th scope="row" valign="top">
            <label for="meta-order"><?php _e( '排序' ); ?></label>
         </th>
         <td>
            <input type="text" name="_term_order" size="3" style="width:10%;" value="<?= get_term_meta( $term->term_id, '_term_order', true ); ?>"/>
         </td>
      </tr>
      </tbody>
   </table>

   <?php
}

/**
 * Save the order value
 *
 * @param int $term_id
 */
add_action( 'edited_category', 'save_term_order' );
function save_term_order( $term_id ) {
   update_term_meta( $term_id, '_term_order', $_POST[ '_term_order' ] );
}

Sort taxonomy terms by the custom field when retrieving them

Once the term meta exists, front-end term queries become simple. Just pass a meta_key and set the ordering method to meta_value_num when calling get_terms().

$args = [
   'meta_key'   => '_term_order',
   'orderby'    => 'meta_value_num',
];

$terms = get_terms( 'category', $args );

If needed, you can also display the sort number in the admin category list with functions such as manage_category_custom_column so editors can see the ordering more clearly in the back end.