Remove All Taxonomies from Post On Update

Question

I've got a custom post type set up with custom taxonomies. When a user updates a post I need a way to check to see if there are any location taxonomies applied and if so then remove them.

I've managed to sort the updating part out. So when post is saved it adds the correct Location taxonomy. I'm using two custom taxonomies on the custom post type too. Locations and Industry. So I need to only check the Location taxonomy and remove any that have been set for that specific post while leaving Industry alone.

Any help would be greatly appreciated. I've checked the WP docs site but found I was getting in a muddle with terms, taxonomy etc.

Answer 1

I think this could be handled with wp_set_object_terms() call on save_post_{$post->post_type} action. Using the post type specific action you'll only target your cpt.

The action provides bool $update parameter, which can be used to check, if the action is fired for a new post or on update.

Passing an empty $terms value to the function clears any existing terms of the set taxonomy, which saves you the effort of first checking, if any terms exist.

// update action to match your custom post type
add_action( 'save_post_{$post_type}', 'my_clear_post_locations_on_update', 10, 3 );
function my_clear_post_locations_on_update(int $post_ID, WP_Post $post, bool $update) {
  // only affect updates, not new post saves
  if ( ! $update ) {
    return;
  }
  // nuke taxonomy terms from the post
  // store return value in a variable for checking the result, if interested
  wp_set_object_terms(
    $post_ID, // object ID
    array(), // terms
    'location', // taxonomy
    false // append
  );
}

P.S. Replace the empty array with a term slug, single term ID, or array of either term slugs or IDs, if you want to force term/s on the post.