Using save_post to replace the post's title

Question

I am using custom posts, and in these, I don't a need for the title.

This causes Wordpress to set the titles of my posts to "Auto Draft".

I'd like to change the title's value to something else, computed from other fields in my post.

How do I go about doing that using save_post or some other means?

Answer 1

I had the exact same need, so I wrote this function - which works. Modify it to your needs. Hope this helps.

// set daily rating title
function set_rating_title ($post_id) {
    if ( $post_id == null || empty($_POST) )
        return;

    if ( !isset( $_POST['post_type'] ) || $_POST['post_type']!='rating' )  
        return; 

    if ( wp_is_post_revision( $post_id ) )
        $post_id = wp_is_post_revision( $post_id );

    global $post;  
    if ( empty( $post ) )
        $post = get_post($post_id);

    if ($_POST['rating_date']!='') {
        global $wpdb;
        $date = date('l, d.m.Y', strtotime($_POST['rating_date']));
        $title = 'TV ratings for ' . $date;
        $where = array( 'ID' => $post_id );
        $wpdb->update( $wpdb->posts, array( 'post_title' => $title ), $where );
    }
}
add_action('save_post', 'set_rating_title', 12 );

Answer 2

Try the filter 'default_title':

add_filter( 'default_title', 'my_default_title', 10, 2 );

function my_default_title( $post_title, $post ){

  $custom_post_type = 'my_awesome_cpt';

  // do it only on your custom post type(s)
  if( $post->post_type !== $custom_post_type )
    return $post_title;

  // create your preferred title here
  $post_title = $custom_post_type . date( 'Y-m-d :: H:i:s', time() );

  return $post_title;
}