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

This simplest method would be to edit the data at the point it's inserted, rather than updating it afterwards, using wp_insert_post_data instead of save_post. This works on creating a new post or updating an existing post without change. It also avoids the danger of creating an infinite loop by triggering update_post within save_post.

add_filter( 'wp_insert_post_data' , 'modify_post_title' , '99', 1 ); // Grabs the inserted post data so you can modify it.

function modify_post_title( $data )
{
  if($data['post_type'] == 'rating' && isset($_POST['rating_date'])) { // If the actual field name of the rating date is different, you'll have to update this.
    $date = date('l, d.m.Y', strtotime($_POST['rating_date']));
    $title = 'TV ratings for ' . $date;
    $data['post_title'] =  $title ; //Updates the post title to your new title.
  }
  return $data; // Returns the modified data.
}

Answer 2

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 3

Here's a solution that uses a static variable to prevent an infinite loop. This allows you to safely call wp_update_post() inside of a function that is hooked to save_post.

function km_set_title_on_save( $post_id ) {

    // Set this variable to false initially.
    static $updated = false;

    // If title has already been set once, bail.
    if ( $updated ) {
        return;
    }

    // Since we're updating this post's title, set this
    // variable to true to ensure it doesn't happen again.
    $updated = true;

    $date           = get_post_meta( $post_id, 'rating_date', true );
    $date_formatted = date( 'l, d.m.Y', strtotime( $date ) );

    // Update the post's title.
    wp_update_post( [
        'ID'         => $post_id,
        'post_title' => 'TV ratings for ' . $date_formatted,
    ] );
}
add_action( 'save_post', 'km_set_title_on_save' );

Note: To limit this functionality to a certain post type, use the save_post_{$post->post_type} hook instead of save_post.

Answer 4

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;
}