Getting categories of posts under a custom taxonomy

Question

I have a CPT with the following taxonomies: category, taxonomy_1 and taxonomy_2 (the last two are non-hierarchical).

I want to get programmatically all the terms of the "category" taxonomy but only of the posts with a given meta value — that meta value is storing the ID of another taxonomy (taxonomy_2).

So it would be: Categories -> Posts -> Specific meta value

I've tried the following without success:

$args = array(
    'meta_query' => array(
        'key'       => 'taxonomy_key_in_CPT',
        'value'     => 'value_of_taxonomy_key_in_CPT',
        'compare'   => "=",
    )
)

$categories = get_categories( $args );

But this will still return all the categories under the CPT. Am I doing something funny?

Answer 1

Welcome to WPSE. I believe you are looking for the get_terms() function. This will return all of the terms for a particular taxonomy, and not the posts.

Pass your taxonomy slug in the array of arguments and set the hide_empty to false so you get a complete list, like this:

$terms = get_terms( array(
    'taxonomy' => 'taxonomy_1',
    'hide_empty' => false,
) );

Full documentation can be found code reference: https://developer.wordpress.org/reference/functions/get_terms/