How to force only one product per order? [duplicate]

Question

I needed to force only one product per order and one amount.

The amount of the product already resolved, now need a solution for just one product per order.

A single product per application, the cart display only one product, where to buy the second notice that it is not possible to purchase more than one product per order

Answer 1

If you've already handled the amount of items per products and you want to restrict the user from adding to cart any additional products, you'll need to listen to an event to manage this. i.e. Can't add Product B, because you already have a Product A in the cart.

There's an event called checkout_cart_add_product_complete that may be suitable. The problem with this is that the product has already been added to the cart at this point.

Your observer would need to handle the following flow:

1. Identify the product that the user tried to add to cart
2. Remove this product from the current cart
3. Add an error message to the session

This should remove the product every single time someone tries to add it to the cart, and then from this point should inform the user that they've exceeded their maximum.

If you've no experience setting up Events and Observers, I'd recommend reading up on the matter:

http://www.solvingmagento.com/events-and-observers-a-magento-tutorial/
http://code.tutsplus.com/tutorials/understanding-magento-observers--cms-21031

Answer 2

My solution was that I added in head.phtml the code below I made:

<?php
$current_page = '';
if(Mage::app()->getFrontController()->getRequest()->getRouteName() == 'cms'):
    $current_page = Mage::getSingleton('cms/page')->getIdentifier();
endif;
if(empty($current_page)):
    $current_page = Mage::app()->getFrontController()->getRequest()->getRouteName();
endif;

if ($current_page == 'checkout') {
    $cartHelper = Mage::helper('checkout/cart');
    $quote = Mage::getSingleton('checkout/session')->getQuote();
    if($quote->getItemsCount() > 1) {
        Mage::getSingleton('core/session')->addError('Message');
        $i = 0;
        foreach ($quote->getAllItems() as $item) {
            $i++;
            if ($i > 1)
                $cartHelper->getCart()->removeItem($item->getId())->save();
                Mage::app()->getResponse()->setRedirect(Mage::helper('core/url')->getCurrentUrl());
        }
    }
}
?>

Answer 3

You can set this in the Product configuration itself under Inventory

Answer 4

Take a look at How to allow only one product in a cart?

You could also try adding an observer for sales_quote_add_item

<sales_quote_add_item>
    <observers>
        <customoptions>
            <type>singleton</type>
            <class>magepal/observer</class>
            <method>checkoutCartProductAddBefore</method>
        </customoptions>
    </observers>
</sales_quote_add_item>

In your observer

.....
public function checkoutCartProductAddBefore($observer)
{
    $quote = Mage::getSingleton('checkout/session')->getQuote();
    if($quote->getItemsCount()>=1){
        Mage::throwException('You can only buy one product at a time.');
    }
}