How to add a category programmatically to a WooCommerce product?

Question

In WooCommerce , if an item is sold out, I would like to add a category "sold out" to it, so that I can show these items in a separate section.

I created the "sold out" category in the WooCommerce / WordPress Admin panel.

This is what I have in my functions.php :

add_action( 'woocommerce_before_shop_loop_item_title', 'mytheme_display_sold_out_loop_woocommerce' );
 
function mytheme_display_sold_out_loop_woocommerce() {
    global $product;
 
    if ( !$product->is_in_stock() ) {
       // add category "sold out"   
    }
}

Now, how can I automatically add the category "sold out" to any sold out WooCommcerce product?

Answer 1

Assuming that the product category term name "sold out" exists, try the following:

add_action( 'woocommerce_before_shop_loop_item_title', 'mytheme_display_sold_out_loop_woocommerce' );
 
function mytheme_display_sold_out_loop_woocommerce() {
    global $product;

    $term_name = 'Sold out';

    // Get the product category term Id for "Sold out" term name
    $term_id   = get_term_by( 'name', $term_name, 'product_cat' )->term_id;
 
    // 1. Add product category "Sold out"
    if ( ! $product->is_in_stock() && ! has_term( $term_id, 'product_cat', $product->get_id() ) ) {
       // Get product categories (if there is any)
       $term_ids = (array) $product->get_category_ids();

       // Add the product category term Id for "Sold out" term name to $term_ids array
       $term_ids[] = $term_id;

       $product->set_category_ids( $term_ids ); // Update product categories
       $product->save(); // Save to database
    } 
    // 2. Remove product category "Sold out"
    elseif ( $product->is_in_stock() && has_term( $term_id, 'product_cat', $product->get_id() ) ) {
       // Get product categories (if there is any)
       $term_ids = (array) $product->get_category_ids();

       // Remove the product category term Id for "Sold out" term name in $term_ids array
       if ( ( $key = array_search( $term_id, $term_ids ) ) !== false ) {
           unset($term_ids[$key]);
       }

       $product->set_category_ids( $term_ids ); // Update product categories
       $product->save(); // Save to database
    }
}

Code goes in functions.php file of your active child theme (or active theme). It should work.

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Now it should be lighter to use the term Id for "sold out" product category, so this way you could replace (in the code) :

$term_name = 'Sold out';

// Get the product category term Id for "Sold out" term name
$term_id   = get_term_by( 'name', $term_name, 'product_cat' )->term_id;

by only the term id for 'Sold out' product category term name like (replace 19 by the real term Id) :

$term_id = 19;