Displaying and getting only the child categories - php

Question

I have a section on my wordpress website that currently displays the child and parent categories of a listing. I would like for only the child categories to be displayed. I wasn't able to figure out the solution on my own, your help is appreciated.
Here is the current code I'm using for this (which also displays parent categories):
<?php
//NEW
$permalink = get_permalink( $id );
//NEW
$seo = get_the_title()." : ";
$Category_links = ' Found in the ';
$term_list_category = wp_get_post_terms(get_the_ID(), 'listings_categories', array("fields" => "ids"));
//THIS CODE REMOVES PARENTS FROM BEING DISPLAYED IN THE LISTING CATEGORIES
foreach ($term_list_category as $k=>$term) {
$children = get_term_children( $term, 'listings_categories');
if ($children)
unset($term_list_category[$k]);
}
$i = 0;
$count = count($term_list_category);
if ( $count > 0 ){
foreach ( $term_list_category as $term_category ) {
$thisCat = get_term_by( 'id', $term_category, 'listings_categories');
//NEW
$url = '<a id="'.$term_category.'" slug="'.$thisCat->{'slug'}.'" class="listing-links-cat" href="#" title="'.$thisCat->{'name'}.'" >'.$thisCat->{'name'}.'</a>';
$i ++;
$seo .= " " . $thisCat->{'name'} . "";
$Category_links .= " " . $url . "";
if($count-1 == $i){
$Category_links .= " and "; $seo .= ", ";
}elseif($count > 1 && $count !== $i){
$Category_links .= ", "; $seo .= ", ";
}
}
$Category_links .= " Categories";
?>
<? echo $Category_links; ?>
But I feel that the overall code can be improved for performance, so it doesn't search the database as much?

Answer 1

Your code is quite ineffecient and also have unnecessary parts to it. Your additional part makes your code even more ineffecient and causes you to hit the db hard.
FLAWS
You get plus 1 for only getting the term id's from the post terms, but unfortunately in this specific case, this tampers your code and this is the starting point of your ineffeciency as you then need to use get_term_by() on every iteration of your foreach loop. This means extra db calls on every iteration for something that should have already been there
The use of get_term_children() adds to the amount of db calls made on every iteration of your foreach loop. Again, you are making unnecessary db calls for something that should have been there in the first place
It is totally unnecessary to count the amount of terms returned by wp_get_post_terms. This adds extra ineffeciency to your code. wp_get_post_terms returns an empty array if no terms exists or a WP_Error object if the taxonomy does not exist. Keep this in mind for later on
SPEEDING IT UP AND STREAMLINING THE CODE
Lets look at what we can do to make your code more effecient
Remove the fields parameter from wp_get_post_terms. As we need more than just the ids of the terms, we need to return the complete term object. You might think that this is ineffecient, but this will save you a lot of db hits and most importantly, time, as you are getting rid of get_term_by() and get_term_children()
There is no proper way to remove parents from wp_get_post_terms(), so the best way will be to just loop over them and ignore/skip them with continue. I assume you are talking about top level terms which have 0 assigned to its $parent property, so you just need to check that the parent value is not 0
Always do proper failure checks. If you don't do that, and your code fails, php error and notices are returned, which is known as bugs. You would want to avoid that. Also, you would always want your code to fail in a controlled, expected manner without bugs. As I stated before, wp_get_post_terms() returns an empty array or a WP_Error object, so this is what you need to check for. If any of these cases occur, immediately halt execution and return the function to avoid bugs and unexpected output
PUTTING THE ABOVE IN CODE
I like to keep my template files short and sweet. For that reason, bulky code the above always goes into a function and I then just call the function in my template files where necessary. Also, just a tip, I have function specific functions files to keep my code organised and not to overload functions.php. my functions.php file is usually not more than 100 lines of code.
For example, this is part of your post's meta, so this will go into a file with other meta functions like displaying the autor name and post date.
function get_post_child_terms( $taxonomy = '' )
{
$current_post = get_queried_object_id();
$terms = wp_get_post_terms( $current_post, $taxonomy );
/*
* Check if $taxonomy has a value, also check for WP_Error or empty $terms. If any of these conditions
* are met, halt execution and return false
*/
if ( !$taxonomy || is_wp_error( $terms ) || empty( $terms ) )
return false;
/*
* We have made it to here safely, now iterate over the terms
*/
foreach ( $terms as $term ) {
/*
* Check for parent terms and ignore them
*/
if ( $term->parent == 0 )
continue;
/*
* Get an array of term names
*/
$term_names[] = $term->name;
}
/*
* Build our string of names
*/
if ( !isset( $term_names ) )
return false;
$string = 'Some text here maybe to start of: ' . implode( ',', $term_names ) . 'Maybe something at the end';
return $string;
}
USAGE
You can now simply call the function in your template as follow:
echo get_post_child_terms( 'listings_category' );
This will produce a list like this
Some text here maybe to start of: Term name 1, Term name 2, Term name 3 Maybe something at the end
FINAL NOTES
The code above is untested and might be a bit buggy.
The code above is the very least that you need. You can extend and misuse it as you see fit to fit your exact needs. A few ideas for extension might be to work in some arguments to where you can choose to display the parent terms or not, and whether the function should return a string of term names or an array of term names. The sky is the limit here
You can build in a cache system to cache your results to optimize these even further.
EDIT
The above code is now tested and is working as expected