saving custom taxonomy as post title

Question

I have two custom taxonomies; "name" and band". The first represents the name of the song, the second represents the band that made the song.

I want to automatically save a combination of those two custom taxonomies in the post title upon saving.

So in the following example: name = "Little Lion Man" band = "Mumford and sons" .. I want the post title to become "Mumford and sons - Little Lion Man"

The code I now have (and works!) is based on this post. However, what this code does is only get one custom taxonomy (in this case the song name, or 'name'). I want to put two custom taxonomy terms in the post title.

This is the code I have now, and I don't know where to begin. I'm not an expert on php.

add_action('save_post', 'update_term_title');
function update_term_title($post_id)
{
    if(defined('DOING_AUTOSAVE') && DOING_AUTOSAVE) 
    return;
if(!current_user_can('edit_post', $post_id))
    return;

$term1 = wp_get_post_terms($post_id, 'name', array('fields' => 'names'));
$term2 = wp_get_post_terms($post_id, 'band', array('fields' => 'names'));

$terms = $term1;

if(empty($terms)) 
    return;

$title = false; 
foreach($terms as $term) 
{
    if($term->parent) 
    {
        $parent = get_term($term->parent, 'name'); 
        $title = $term->name.' '.$parent->name;
        break;
    }
}
/*Default to first selected term name if no children were found*/
$title = $title ? $title : $terms[0]->name;

/*We must disable this hook and reenable from within
if we don't want to get caught in a loop*/
remove_action('save_post', 'update_term_title');
$update = array(
    'ID'=>$post_id,
    'post_name'=>sanitize_title_with_dashes($title),
    'post_title'=>$title
);
wp_update_post($update);
add_action('save_post', 'update_term_title');
}

Does anyone have a suggestion on how to make this work? It should be a minor modification of the code. Maybe make two loops?

Answer 1

Updated Answer:

You're trying to mix a lot of things that you don't understand, by using the $args in wp_get_post_terms you don't need to run the foreach to hunt for child terms (is your custom taxonomy even hierarchical anyway?). As a catch-all you can just implode the whole list and get the same result (but without seeing/knowing your schema I can't be sure it's actually what you want.)

<?php
add_action('save_post', 'update_term_title');
function update_term_title($post_id) {
    if (defined('DOING_AUTOSAVE') && DOING_AUTOSAVE) return;
    if (!current_user_can('edit_post', $post_id)) return;

    $names = wp_get_post_terms($post_id, 'name', array('fields' => 'names'));
    // $names == array( 0 => 'name1'[, 1 => 'name2'[, 2 => ...]])
    $bands = wp_get_post_terms($post_id, 'band', array('fields' => 'names'));
    // $bands == array( 0 => 'band1'[, 1 => 'band2'[, 2 => ...]])

    // collapse parent and child terms
    $name = implode(' ', $names);
    // $name == "name1[ name2[ ...]]"
    $band = implode(' ', $bands);
    // $band == "band1[ band2[ ...]]"

    if ($name OR $band) {
        // concat name and band, use trim to clean the string if one is missing
        $title = trim(implode(' ', array($name, $band)));
        // $title == "name1[ name2[ ...]] band1[ band2[ ...]]"
        // disable and reenable hook from within to avoid a loop
        remove_action('save_post', 'update_term_title');
        $update = array(
            'ID' => $post_id,
            'post_name' => sanitize_title_with_dashes($title),
            'post_title' => $title,
        );
        wp_update_post($update);
        add_action('save_post', 'update_term_title');
    }
}

Normally I wouldn't suggest this method because of the disable/reenable hack, there is a filter for post data called wp_insert_post_data meant for altering the post data prior to the DB UPDATE/INSERT, but you'd probably have to understand quite a bit more to get past figuring out how to reference the taxonomy items that haven't yet been saved. The above method is technically quite expensive as it requires saving a post, requesting the post and then saving the post again

Old Answer:

wp_get_post_terms() returns an array, not a string. wp_get_post_terms docs

You need to treat $term1 and $term2 as arrays.

$term1 = wp_get_post_terms($post_id, 'name', array('fields' => 'names'));
$term2 = wp_get_post_terms($post_id, 'band', array('fields' => 'names'));
# this assumes the first term in the taxonomy is the one you want
$terms = array_pop($term1) . array_pop($term2);