Match tag names with form titles

Question

I am trying to match tag names with form titles to fetch the correct form into the current post, to subscribe to new posts tagged with the current posts tag. I only have 1 tag assigned per post.

The code for categories works well, and I tried to transcribe it for tags, but I am afraid there are syntax errors in the code, because it does not work.

How do I write the correct code?

add_shortcode( 'subscribe-to-tag', function() {
   global $wpdb, $post;
 
$the_tag = get_the_tags( $post->ID );
$tag_name = $the_tag[0]->tag_name;
   $id = $wpdb->get_var($wpdb->prepare("SELECT ID FROM wptq_forms WHERE name = '{$tag_name}';"));
   if (is_null($id)) { return ''; }
   return do_shortcode( '[newsletter_form id="' . intval( $id ) . '"]' );
} ); 

Answer 1

I don't see PHP syntax errors (like unwanted brackets) in your code, but there are two WordPress-specific issues that need to be fixed:

1. Note that wpdb::prepare() needs one or more placeholders (e.g. %s for strings and %d for numbers) and the replacement value for each placeholder.

   So in your case, the correct $wpdb->prepare() would be:

   $wpdb->prepare( "SELECT ID FROM wptq_forms WHERE name = %s", $tag_name );
   

2. get_the_tags() returns an array of term objects on successful requests, and each object is a WP_Term instance which does not have a tag_name property, only name.

   Therefore $the_tag[0]->tag_name should instead be $the_tag[0]->name.