Update permalinks when new category added to custom post type taxonomy

Question

Note: this question also appears on https://stackoverflow.com/questions/44060613/update-permalinks-when-new-category-added-to-custom-post-type-taxonomy (but is not getting much love).

Have created a collection of Custom Post Types (CPT) for a WordPress theme I am working on (along with their own taxonomies and tags). For the purpose of this question I will just focus on the 'projects' CPT.

When a new project category is added, and then linked to in the navigation menu - the user will see a 404 error until permalinks are saved, clearing WordPress' route caching.

I was thinking the best way to achieve this would be to use flush_rewrite_rules();

Although, saying that - I don't take it lightly as best practice strongly recommends only using this function when activating/deactivating a plugin. https://codex.wordpress.org/Function_Reference/flush_rewrite_rules#Usage

What I want to do is hook into the action that fires when a new CPT category is created (either via the post or admin screen) and then run the flush rewrite upon that action so that the WP admin doesn't have to concern themselves with forcing Wordpress route caching via update on permalinks.

I looked at this Hook onto Add New Category for a possible solution and attempted to use this code:

function custom_created_term( $term_id, $tt_id, $taxonomy )
{
    $project_cpt = 'CPT_PROJECT';  // Edit this to your needs
    $project_tax = 'TAX_PROJECT_CATS';  // Edit this to your needs

    if( DOING_AJAX && $project_tax === $taxonomy )
    {
        // Try to get the post type from the post id in the referred page url
        // Example: /wp-admin/post.php?post=2122&action=edit&message=1

        parse_str( parse_url( wp_get_referer(), PHP_URL_QUERY ) , $params );

        if( isset( $params['post'] ) )
        {
            $post_id = intval( $params['post'] );
            if( $post_id > 0 && $project_cpt === get_post_type( $post_id ) )
            {
                flush_rewrite_rules(true);

            }
        }
    }
}

But it is not really working out for me. Not sure if I am using the right tool here or if I am doing something wrong. Have searched quite a bit to the solution but I haven't come up with a good solution to my problem here (can't find the hook for creating new CPT categories).

Answer 1

That's not how custom taxonomies and post types work

This is what you do:

• On the init hook, call register_custom_taxonomy or register_post_type
• If you change your calls to register_custom_taxonomy or register_post_type, or add new ones in your code, regenerate permalinks by visiting the permalinks settings page and clicking save
• You're done

So if I follow the above steps and create a new taxonomy named colour, I do not need to flush permalinks to create red or blue terms. If I created a brand new taxonomy named shape I would flush the permalinks, but only once, this is so that I don't get 404's when I visit shape terms on the frontend. The same is true of custom post types

Keep in mind that flush_rewrite_rules is a very expensive function, and you should never need to call it. An example of when it might be called is in a plugins activation hook after it's first installed, or a WP CLI command.

How To Avoid The 404's

Use register_activation_hook to flush rewrite rules. This will get called when your plugin is activated ( and only the time it's activated, not every page load ).

https://codex.wordpress.org/Function_Reference/register_activation_hook

Flushing on the creation of every term is both unnecessary, and damaging

What If I Registered My CPT/CT In A Theme?

You can use the after_theme_switch hook to flush rewrite rules, however, registering post types and taxonomies in a theme is bad practice. It causes issues with data portability, e.g. if a user changes themes they loose their data.

Themes determine how a site looks, and functionality, especially data, should be defined in plugins.

Answer 2

Ok, pretty simple solution I came up with. Just put this code below into my includes within function.php:

add_action('wp_update_nav_menu_item', function ()
{
    flush_rewrite_rules(true);
}, 10, 2);

This just hooks into the nav menu update function, so it fires every time menu is updated by admin user.

I know flush rewrite is an "expensive" function but it will only be called when the navigation menu is updated which will not be all that often.