Change auto post title generation according to different post properties

Question

I have the following snippet that allows me to auto generate the post title. I'd like to change the $post_type of the 'post_title' => $post_type . ' Job #' . $post_id line to some other post property like post_date and post_author.

function save_post_func_2134( $post_id ) {     
    $post_type = 'post'; //Change your post_type here     
    if ( $post_type == get_post_type ( $post_id ) ) {  //Check and update for the specific $post_type         
        $my_post = array(
            'ID'           => $post_id,
            'post_title' => $post_type . ' Job #' . $post_id //Construct post_title 
        );
         remove_action('save_post', 'save_post_func_2134'); //Avoid the infinite loop 
        // Update the post into the database
        wp_update_post( $my_post );              
    }
}
add_action( 'save_post', 'save_post_func_2134' );

Answer 1

The post object is passed by reference as the second parameter of the save_post action (do_action ( 'save_post', int $post_ID, WP_Post $post, bool $update ). You can use this post object to get the post date and author from.

You can try the following: (NOTE: The code is untested)

add_action( 'save_post', 'wpse_214927_alter_title', 10, 2 );
function wpse_214927_alter_title ( $post_id, $post_object )
{
    // Target only specific post type
    if (    'my_specific_post_type'       !== $post_object->post_type
         && 'my_other_specific_post_type' !== $post_object->post_type
    )
        return;

    // Remove the current action
    remove_action( current_filter(), __FUNCTION__ );

    $post_date      = $post_object->post_date;
    $format_date    = DateTime::createFromFormat( 'Y-m-d H:i:s', $post_date );
    $date_formatted = $format_date->format( 'Y-m-d' ); // Set correct to display here
    $post_author    = $post_object->post_author;
    $author_name    = get_the_author_meta( 'display_name', $post_author ); // Adjust as needed

    $my_post = [
        'ID' => $post_id,
        'post_title' => $author_name . ' Job ' . $date_formatted // Change as needed
    ];
    wp_update_post( $my_post );
}

Just an important note, you should add validation and sanitation where needed

Answer 2

Use the function get_post_meta($post_id) to get the post meta data.

Hope this helps.