Show date as permalink for custom post type instead of post name

Question

I created a custom post type and specified a rewrite to change the permalink to /old-donuts/. See code below:

function donut_newsletters_post_type() {

  $labels = array(
    'name' => '🍩 Newsletters',
    'singular_name' => '🍩 Newsletter',
    'add_new' => 'Add 🍩',
    'add_new_item' => 'Add New 🍩',
    'edit_item' => 'Edit 🍩',
    'new_item' => 'New 🍩',
    'view_item' => 'View 🍩',
    'search_item' => 'Search Daily 🍩s',
    'not_found' => 'No 🍩s found',
    'not_found_in_trash' => 'NO 🍩s found in the trash..that would be a sin'
  );
  $args = array(
    'labels' => $labels,
    'public' => true,
    'has_archive' => false,
    'publicly_queryable' => true,
    'query_var' => true,
    'rewrite' => array(
      'slug' => 'old-donuts'
    ),
    'capability_type' => 'post',
    'hierarchical' => false,
    'supports' => array(
      'title',
      'editor',
      'excerpt',
      'thumbnail'
    ),
    'taxonomies' => array('post_tags'),
    'menu_position' => 0,
    'exclude_from_search' => true,
    'menu_icon'   => 'dashicons-email'
  );

  register_post_type('donut_newsletters', $args);
}

add_action('init', 'donut_newsletters_post_type');

Now let's say I go create a new post and title it "test", the permalink defaults to https://thedonut.co/old-donuts/test

I don't want this. What I do want is for the permalink to instead default to a custom date structure like this:

https://thedonut.co/old-donuts/2019-08-24/

I also want the keep the permalink modifiable by the editor so that in the case that he/she had to create a post the day before they want it to go live, they can change the day value to the next day.

Please don't send me to a plugin. I've tried custom post type permalinks plugin and it does what i want, but it doesn't allow modification of the permalink after the post is published.

Answer 1

One thing you can do is pre-set the post_name field using the wp_insert_post_data hook. The field passes 2 variables: $data which is the initial default data and $postedarr which is what's given whenever the post is $_POSTed, updated, or published.

/**
 * Modify the postdata before it's inserted into the database
 *
 * @param Array $data
 * @param Array $postarr
 *
 * @return void
 */
function wpse345850_modify_postdata( $data, $postarr ) {

    if( 'post' != $data['post_type'] || $postarr['ID'] ) {  // A $_POSTed ID means it's an update, not new
        return $data;
    }

    $data['post_name'] = date( 'Y-m-d' );

    return $data;

}
add_filter( 'wp_insert_post_data', 'wpse345850_modify_postdata', 10, 2 );

Note that you'll have to change the above post type from post to your desired post type.