Returning custom taxonomy in slug order - php

Question

I have a loop to pull in custom taxonomy terms that I'd like to order by slug, but when I add in the 'orderby' command my loop is broken and returns nothing. No doubt I'm using incorrect syntax, but I can't see where for the life of me!
<?php
$loop = new WP_Query(
array(
'post_type' => 'camp',
'orderby' => 'name',
'order' => 'ASC',
'tax_query' => array(
array(
'taxonomy' => 'types',
'field' => 'slug',
'terms' => $term->slug,
),
)
)
);
if ($loop->have_posts()) :
while ($loop->have_posts()) : $loop->the_post();
$terms = get_lowest_taxonomy_terms(get_the_terms( get_the_ID(), array(
'taxonomy' => 'destinations',
'orderby' => 'slug',
'order' => 'ASC'
)) );
?>
Any help would be very much appreciated :)
Added additional function:
The get_lowest_taxonomy_terms is running as follows:
get_lowest_taxonomy_terms( $terms ) {
// if terms is not array or its empty don't proceed
if ( ! is_array( $terms ) || empty( $terms ) ) {
return false;
}
$filter = function($terms) use (&$filter) {
$return_terms = array();
$term_ids = array();
foreach ($terms as $t){
if( $t->parent == 0 ) {
$term_ids[] = $t->term_id;
}
}
foreach ( $terms as $t ) {
if( $t->parent == false || !in_array($t->parent,$term_ids) ) {
//remove this term
}
else{
$return_terms[] = $t;
}
}
if( count($return_terms) ){
return $filter($return_terms);
}
else {
return $terms;
}
};
return $filter($terms);
}
Desired Output
The loop should query the taxonomy type 'destination', where that destination has the additional taxonomy of 'type'.
Screen grab of the current output:
The results are ordered into 3 cols by CSS, but as you can see, not sorting alphabetically.

Answer 1

get_the_terms doesn't take an array as second parameter.
get_the_terms( int|object $post, string $taxonomy )
Parameters:
$post (int|object) (Required) Post ID or object.
$taxonomy (string) (Required) Taxonomy name.
More details of get_the_terms
By default, get_the_terms doesn't have any sorting option. But, you can use usort to sort the returned array.
So, your last part of the code should be:
$terms = get_lowest_taxonomy_terms(get_the_terms( get_the_ID(), 'destinations' ));
This is a quick example of how you can sort it using usort:
$terms = get_the_terms( get_the_ID(), 'destinations' );
usort($terms,"so980_sort_terms_alphabetically");
function so980_sort_terms_alphabetically($a,$b) {
return $a['slug'] > $b['slug'];//using 'slug' as sorting order
}
so980_sort_terms_alphabetically function should be in your theme's functions.php file.
So finally, your last part will become:
$terms = get_the_terms( get_the_ID(), 'destinations' );
usort($terms,"so980_sort_terms_alphabetically");
$terms = get_lowest_taxonomy_terms($terms);
Update
I have just tested it, and it is returning a fatal error, as I have made a mistake. Error message: Fatal error: Cannot use object of type WP_Term as array.
get_the_terms returns an object. So, using $a['slug'] was causing the error.
Here, so980_sort_terms_alphabetically should be implemented in following way:
function so980_sort_terms_alphabetically($a,$b) {
return $a->slug > $b->slug;//using 'slug' as sorting order
}
**This is tested, and working.
Update 2
Since your output codes are not available in your question, I will assume that you are printing inside the loop. Instead of doing that, we will save returned terms in another array, and sort it outside the loop, so that we can get all of the terms at once.
Here is a quick example of how you can do it:
if ($loop->have_posts()) :
while ($loop->have_posts()) : $loop->the_post();
$pre_terms = get_lowest_taxonomy_terms(get_the_terms(get_the_ID(), 'product_tag'));
if ( $pre_terms ) {
foreach ( $pre_terms as $pre_term ) {
$terms[] = $pre_term;
}
}
endwhile;
endif;
usort($terms,"so980_sort_terms_alphabetically");
//a quick test to see if it's working or not
foreach ( $terms as $term ) {
echo $term->slug;
echo '<br/>';
}