Values inside a custom field to determine which category posts to display

Question

I am facing a little problem whilst trying to display posts, from certain categories, on the front end. I've created a custom field whose key is 'related_categories' and I've different categories with slugs such as 'army', 'navy', 'airforce' etc.

When creating a new custom post, I enter the slugs of different categories inside the 'related_categories' custom field, for e.g. 'navy', 'airforce', and this is the code which I've inside my template file to echo the custom field values inside the 'tax_query' array.

<?php global $post;

$related = array ( get_post_meta($post->ID, 'related_categories', true) );

$the_query = new WP_Query( array( 'post_type' => 'medals', 'posts_per_page' => 3, 'tax_query' => array( array( 'taxonomy' => 'medal-categories', 'field' => 'slug', 'terms' => $related, ), ), ) ); 

while ( $the_query->have_posts() ) : $the_query->the_post(); 

//loop starts after this

Now the problem which I am facing is that if I enter only one slug inside the 'related_categories' custom field, for e.g. 'navy', then the posts from the 'navy' category successfully show up but if I enter more than one slug inside the 'related_categories' custom field, for e.g. 'navy', 'army', then the posts do not show up.

I tried searching for a solution on the internet but couldn't find any therefore any help would be appreciated. Thank you.

Answer 1

The problem is that you are passing a comma separated list of terms, not an array of term. For example, if you enter 'army,navy,airforce' in the custom field:

$related = array ( get_post_meta($post->ID, 'related_categories', true) );
//$related = array('army,navy,airforce');
//What you need is
//$related = array('army','navy,'airforce');

You need to transform each term into a array member, for example using explode:

$related = explode(',', trim( get_post_meta($post->ID, 'related_categories', true) ) );

Anyway, I think that you should think in another way to get your purpose. Using a custom field to manual store a list a related categories is not appropiate from my point of view. You could created, for example, a hierarchical taxonomy and set related categories under the same parent, or use the core tag taxonomy to set relationships, etc, I think this is better and more "natural" than using a custom field to store a set of taxonomy terms.