Magento 2 – Share Cart in Multistore

Magento does not allow sharing carts between websites. The sessions objects for individual websites are completely detached, products in one website may not belong to the other website, the category structure and visibility of data will be different. As you pointed out, the pricing may be different from one website to another as well, as could the promotions, tax rates, etc.

From a data perspective, it would be rather difficult to share carts between websites given that a product you may have in your cart may or may not be in the next website you go to. This would create major problems with products disappearing and/or errors in the cart due to products not being available.

Something like this would have to be completely custom built, and I'm certain it would not come without it's problems and anomalies.

Without knowing more to contextualize the situation, I'm skeptical that using multiple websites with different prices and currencies plus sharing the cart between them is the best solution. If the pricing and the currencies are different, why do the carts even need to be shared? Doesn't make sense to me, and I'm having a hard time imagining a scenario where this would be appropriate. Perhaps you could enlighten us.

To share cart among websites you have to do two things.

1. Make Magento 2 read cart quote id from a single session key.

   class Session extends \Magento\Checkout\Model\Session
   {
       /**
        * @return string
        */
       protected function _getQuoteIdKey()
       {
           return 'quote_id_1';
       }
   }
   

2. Make Magento consider all stores when loading quote

   class QuoteRepository extends \Magento\Quote\Model\QuoteRepository
   {
       /**
        * Load quote with different methods
        * Will consider all stores valid, quote can be shared among all stores.
        *
        * @param string $loadMethod
        * @param string $loadField
        * @param int $identifier
        * @param int[] $sharedStoreIds
        * @throws NoSuchEntityException
        * @return Quote
        */
       protected function loadQuote($loadMethod, $loadField, $identifier, array $sharedStoreIds = [])
       {
           $sharedStoreIds = $this->getStoreIds();
   
           /** @var Quote $quote */
           $quote = $this->quoteFactory->create();
           if ($sharedStoreIds) {
               $quote->setSharedStoreIds($sharedStoreIds);
           }
           $quote->setStoreId($this->storeManager->getStore()->getId())->$loadMethod($identifier);
           $quote->setStoreId($this->storeManager->getStore()->getId())->load($identifier);
           if (!$quote->getId()) {
               throw NoSuchEntityException::singleField($loadField, $identifier);
           }
           return $quote;
       }
   
   
       /**
        * @return int[]
        */
       protected function getStoreIds()
       {
           $storeIds = [];
           $stores = $this->storeManager->getStores();
   
           foreach ($stores as $storeId => $store) {
               $storeIds[] = $storeId;
           }
   
           return $storeIds;
       }
   }