How to use a specific custom field in a custom post type as slug

Question

I'd like use a specific custom field in a custom post type as the slug for the post.

My custom post type is members and the custom field that I want to use as the slug is member_user. How can I do this?

Answer 1

You could do this like saving post meta. You would unhook out of the current hook and update the post, if you don't do that you will end up in an infinite loop:

/**
 * Save Custom Data
 * @param int $post_id
 * @param Post Object $post
 */
function save_custom_meta_boxes( $post_id, $post ) {

    // If we're not in the right place, bailout
    if( ! isset( $post ) || wp_is_post_autosave( $post ) || wp_is_post_revision( $post ) ) {
        return $post_id;
    }

    // `members` Type Metaboxes
    if( 'members' == $post->post_type ) {

        // Update Post Slug
        if( isset( $_POST['member_user'] ) && ! empty( $_POST['member_user'] ) ) {
            remove_action( 'save_post', 'save_custom_meta_boxes' );
            wp_update_post( array( 'ID' => $post_id, 'post_name' => sanitize_title( $_POST['member_user'] ) ) );
            add_action( 'save_post', 'save_custom_meta_boxes' );
        }
    }
}
add_action( 'save_post', 'save_custom_meta_boxes', 10, 2 );

IF the user has set a value into the member_user field we will remove the current action, update the post to the new slug using the same field, and rehook the action to continue processing any other post meta values. We take advantage of sanitize_title() to ensure the user doesn't add anything malicious.