Woocommerce – Prevent Adding items from two different categories to cart

2 comments

1. I’ve solved this before. My write-up is here.

   It differs slightly from your request in that instead of clearing the cart when they try to add a second category it keeps the original item in the cart and displays a warning.

   For posterity:

   <?php
   
   // Enforce single parent category items in cart at a time based on first item in cart
   function get_product_top_level_category ( $product_id ) {
   
       $product_terms            =  get_the_terms ( $product_id, 'product_cat' );
       $product_category_term    =  $product_terms[0];
       $product_category_parent  =  $product_terms[0]->parent;
   
       while ( $product_category_parent  !=  0 ) {
               $product_category_term    =  get_term($product_category_parent, 'product_cat' );
               $product_category_parent  =  $product_category_term->parent;
       }
   
       return $product_category_term;
   
   }
   
   add_filter ( 'woocommerce_before_cart', 'restrict_cart_to_single_category' );
   function restrict_cart_to_single_category() {
           global $woocommerce;
           $cart_contents    =  $woocommerce->cart->get_cart( );
           $cart_item_keys   =  array_keys ( $cart_contents );
           $cart_item_count  =  count ( $cart_item_keys );
   
           // Do nothing if the cart is empty
           // Do nothing if the cart only has one item
           if ( ! $cart_contents || $cart_item_count == 1 ) {
                   return null;
           }
   
           // Multiple Items in cart
           $first_item                    =  $cart_item_keys[0];
           $first_item_id                 =  $cart_contents[$first_item]['product_id'];
           $first_item_top_category       =  get_product_top_level_category ( $first_item_id );
           $first_item_top_category_term  =  get_term ( $first_item_top_category, 'product_cat' );
           $first_item_top_category_name  =  $first_item_top_category_term->name;
   
           // Now we check each subsequent items top-level parent category
           foreach ( $cart_item_keys as $key ) {
                   if ( $key  ==  $first_item ) {
                           continue;
                   }
                   else {
                           $product_id            =  $cart_contents[$key]['product_id'];
                           $product_top_category  =  get_product_top_level_category( $product_id );
   
                           if ( $product_top_category  !=  $first_item_top_category ) {
                                   $woocommerce->cart->set_quantity ( $key, 0, true );
                                   $mismatched_categories  =  1;
                           }
                   }
           }
   
           // we really only want to display this message once for anyone, including those that have carts already prefilled
           if ( isset ( $mismatched_categories ) ) {
                   echo '<p class="woocommerce-error">Only one category allowed in cart at a time.<br />You are currently allowed only <strong>'.$first_item_top_category_name.'</strong> items in your cart.<br />To order a different category empty your cart first.</p>';
           }
   }
   ?>
   

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2. Here is my solution for this (You can replace ‘city’ by ‘product_cat’ to make it work for product categories:

   function validate_add_cart_item( $passed, $product_id, $quantity, $variation_id = '', $variations= '' ) {
   
       // Get the list of cities for the item to be added
       $product_cities = get_the_terms( $product_id, 'city' );
       $cities_array = array_map(function($city){
           return $city->slug;
       }, $product_cities);
   
       // Get the cart items
       $item_in_cart = WC()->cart->get_cart();
   
       // Check for each item if the city is different
       foreach ($item_in_cart as $item){
           $cities = get_the_terms( $item['product_id'], 'city' );
           foreach ($cities as $city){
               if(!in_array($city->slug, $cities_array)){
                   $passed = false;
                   wc_add_notice( __( 'You cannot mix products from two cities', 'domain' ), 'error' );
               }
           }
       }
   
       return $passed;
   }
   add_filter( 'woocommerce_add_to_cart_validation', 'validate_add_cart_item', 10, 5 );
   

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