WP_Query get posts from custom posts by category

Question

ive been playing around with this for ages and for some reason I cant get it to work.

This is from within the single post page of a custom post type...

Basically I am getting the category of the custom post type by using the get_the_term and then doing a foreach to nicely input into a string.

I then use a WP_Query to retrieve, but I think I have the logic wrong.

This is what I have

// post types query
if ( have_posts() ) : while ( have_posts() ) :the_post();

// getting the categories
$categorynames = '';
$getcategory = get_the_terms($post->ID, 'custompostnamehere-categories');

foreach($getcategory as $t){ $categorynames .= $t->term_id.' ,';}

if (substr($categorynames, -1) == ',') {
$categorynames = substr($categorynames, 0, -1);
}

// end of post type query
endwhile; endif; wp_reset_query(); 

//starting new query to get related posts within the same categories
$args = array(
  'post_type' => 'custompostnamehere',
  'cat' => $categorynames,
  'posts_per_page' => 20
);
$q = new WP_Query($args);

// retrieving the data
while($q->have_posts()){

}

Could someone please enlighten me on my wrong doings.

Thanks

Answer 1

You're using category query for your custom taxonomy. So it won't work, because there are no categories with such IDs.

You should use tax_query instead.

// post types query
while ( have_posts() ) {
    the_post();

    // getting the categories
    $categoryIDs = array();  // it's much nicer than concatenated string
    $getcategory = get_the_terms($post->ID, 'custompostnamehere-categories');

    foreach($getcategory as $t) {
        $categoryIDs[] = $t->term_id;
    }

// end of post type query
}
// resetting query isn't needed - you will call your own query next

//starting new query to get related posts within the same categories
$args = array(
    'post_type' => 'custompostnamehere',
    'tax_query' => array(
        array( 
            'taxonomy' => 'yourcustomtaxonomy',
            'field' => 'id',
            'terms' => $categoryIDs
        )
    ),
    'posts_per_page' => 20
);
$q = new WP_Query($args);

// retrieving the data
while( $q->have_posts() ) {
    $q->the_post();
    ...
}