How to verify if blog post don’t have any categories in WordPress

In my current work I have to solve many problems for customers with WordPress websites. It’s common to see this scenario:

• Website running a child theme based on Twenty something WP Theme
• A thousand plugins installed, half active, half inactive
• Patches all over functions.php
• Custom plugins
• A mess in the way they created .php files

And then they want to implement something which might not be that hard, but it takes 5 hours to find out where is this function calling, which hook is doing what, which file has the content of this nonsense piece of code, etc.

Today I had to face this situation: the customer has a website to display products, most of them are linked to a category, but some of them don’t, and they want to display a generic category under those products.

In order to fix this, I had to implement an if statement to check whether the post has a category or not, in case it has, leave the old code running to display the proper category, and if not, display a custom message with a link to the generic category. Bla bla.

This is the code that allowed me to do that:

<?php

$terms = get_the_term_list( $post->ID, 'categories', '<li class="item">', ' . ', '</li>' );

echo $terms;

if(empty($terms)){
echo '<li class="collection_item"><a href="#">Generic Title</a></li>';
}

?>

I just had to use the get_the_term_list(); WP function explained here.