Woocommerce – Prevent Adding items from two different categories to cart

I want to prevent users from adding products from different categories into cart at once. Say if the user navigates to another categories and tries to add product to cart, they get the cart cleared out first. Please anybody know how i might approach this? I am a newbie at things like this. Thanks

Answer

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>';
        }
}
?>