Listing Child categories under another child category

Question

I have a custom post type called "alz-products" under this i also have a taxonomy called "products-category"

The arranged category structure to manage products as follows

Spill Kits
|
|
|
|------ Chemical
        |
        |------ 15 to 120 Liters
        |------ 660 to 1100 Liters
        |------ 80 to 360 Liters

As you can see "Spill Kits" is the main parent category here under that there is child category "Chemical", then under "Chemical" there are child categories like "15 to 120 Liters" etc.

Basically "Spill kits" have more categories like "Chemical" which also have child categories under those. What i want is a way to list all the child categories under the child categories of parent on the main category page.

for example I want to list 15 to 120 Liters, 660 to 1100 Liters, 80 to 360 Liters on "Spill kits" page (ones makred as Child categories of Chemicals in the image below). no need of showing "Chemical" at all.

I have only able to list main child categories using this so far

$term_children = get_terms( array( 'taxonomy' => 'products-category', 'parent' => get_queried_object_id(), ) );

if ( ! is_wp_error( $terms ) ) {
foreach ( $term_children as $child ) {
 echo '
 <div class="product-archive">
  <div class="post-title">
 <h3 class="product-name"><a href="' . get_term_link( $child ) . '">' . $child->name . '</a></h3>
  </div>
  </div>
 ';
}
}

Answer 1

The missing part from what you've written in code is the idea of putting extra foreach loops inside the foreach loop you already have to go one level deeper. Likewise recursion would have solved this, but it's unlikely it would have been helpful once it was revealed what you were trying to build.

• foreach child term
  • print that child term
  • fetch the grandchildren, aka the children of the child term
  • foreach grandchild term
    • print the grandchild term
    • fetch the great-grandchildren, aka the children of the grandchild term
    • foreach great-grandchild term
      • print the great-grandchild term
      • fetch the great-great-grandchildren aka the children of the great-grandchild term
      • foreach great-great-grandchild term
        • print the great-great-grandchild term
        • etc etc

Notice how each loop does the same thing but is nested one level deeper?

For example this prints out a list of child terms, with sub-lists of grandchild terms:

// ## display the child terms
$child_terms = get_terms( [
    'taxonomy' => 'products-category',
    'parent' => get_queried_object_id(),
] );
if ( ! is_wp_error( $child_terms ) ) {
    echo '<ul>';
    foreach ( $child_terms as $child_term ) {
        echo '<li>' . $child_term->name . '</li>';

        // ### display the grandchild terms
        $grandchild_terms = get_terms( [
            'taxonomy' => 'products-category',
            'parent'   => $child_term->parent,
        ] );
        if ( ! is_wp_error( $grandchild_terms ) ) {
            echo '<ul>';
            foreach ( $grandchild_terms as $grandchild_term ) {
                echo '<li>' . $grandchild_term->name . '</li>';

                // #### display the great-grandchild terms.. etc
                $greatgrandchild_terms = get_terms( [
                    'taxonomy' => 'products-category',
                    'parent' => $grandchild_term->parent,
                ] );
                if ( ! is_wp_error( $greatgrandchild_terms ) ) {
                    // etc...


            }
            echo '</ul>';
        }
        echo '</ul>';
    }
}

You could add additional loops inside the deepest foreach to grab 3, 4, or more levels deeper.

Note that earlier I mentioned recursion, this would allow you to write a single function that went infinitely deep, but this probably won't help you since you want to display each level using different HTML in different places.

For example:

function display_product_categories_as_list( int $term_id ) : void {
    $child_terms = get_terms( [
        'taxonomy' => 'products-category',
        'parent'   => $term->term_id,
    ] );
    if ( ! is_wp_error( $child_terms ) ) {
        echo '<ul>';
        foreach ( $child_terms as $child_term ) {
            echo '<li>' . $child_term->name . '</li>';
            display_product_categories_as_list( $child_term );
        }
    }
}

display_product_categories_as_list( get_queried_object_id() );

That would display the entire tree of terms as a list with child terms indented, but they would all be displayed the same, and it would go past 3 levels. Notice the function calls itself inside the loop, this is a basic form of recursion. Instead manual nested loops would work better for your use case.