title: Allow only one item in cart from defined product categories in Woocommerce
body: <p>In Woocommerce, I found a bit of code that restricts a users purchase to one per category for category a or b. So currently the user could purchase 2 items 1 from cat a and 1 from cat b. I would like to limit the user to only one product from category a or b. The code I am working with is below, thanks in advance.</p>
  
  <pre><code>add_filter( 'woocommerce_add_to_cart_validation', 'allowed_quantity_per_category_in_the_cart', 10, 2 );function allowed_quantity_per_category_in_the_cart( $passed, $product_id) {
  
  $max_num_products = 1;// change the maximum allowed in the cart
  $running_qty = 0;
  
  $restricted_product_cats = array();
  
  //Restrict particular category/categories by category slug
  $restricted_product_cats[] = 'cat-a, cat-b';
  
  
  // Getting the current product category slugs in an array
  $product_cats_object = get_the_terms( $product_id, 'product_cat' );
  foreach($product_cats_object as $obj_prod_cat) $current_product_cats[]=$obj_prod_cat-&gt;slug;
  
  
  // Iterating through each cart item
  foreach (WC()-&gt;cart-&gt;get_cart() as $cart_item_key=&gt;$cart_item ){
  
      // Restrict $max_num_products from each category
      if( has_term( $current_product_cats, 'product_cat', $cart_item['product_id'] )) {
  
      // Restrict $max_num_products from restricted product categories
      //if( array_intersect($restricted_product_cats, $current_product_cats) &amp;&amp; has_term( $restricted_product_cats, 'product_cat', $cart_item['product_id'] )) {
  
          // count(selected category) quantity
          $running_qty += (int) $cart_item['quantity'];
  
          // More than allowed products in the cart is not allowed
          if( $running_qty &gt;= $max_num_products ) {
              wc_add_notice( sprintf( 'Only %s '.($max_num_products&gt;1?'products from this category are':'product from this category is').' allowed in the cart.',  $max_num_products ), 'error' );
              $passed = false; // don't add the new product to the cart
              // We stop the loop
              break;
          }
  
      }
  }
  return $passed;}
  </code></pre>