How to add condition in add-to-cart button function? Magento 1.9

Question

How to Add PHP script in add-to-cart function like if other products are trying to add add-to-cart, supposed selected id based products[restricted products] already available in add-to-cart here restrict and show message like not allowed to add-to-cart, please purchase alone, if already some other products available in cart condition like you need to purchase this product alone.

Using Magento add-to-cart button Function how to achieve my above condition?

• Ketan Borada: magento.stackexchange.com/questions/279094/…

Answer 1

Create an event observer for event sales_quote_merge_before. Create a custom module and put this in config.xml.

<events>
 <sales_quote_merge_before>
 <observers>
 <cart_validation>
 <class>MyModule_CartValidation_Model_Observer</class>
 <method>quoteMergeBefore</method>
 </cart_update>
 </observers>
 </sales_quote_merge_before>
</events>

Create Observer.php in [MyModule]/[CartValidation]/Model and put this code.

class MyModule_CartValidation_Model_Observer {
 public function quoteMergeBefore($observer) {
 // Get Existing Cart Items
 $quoteItem = Mage::getSingleton('checkout/cart') - > getQuote() - > getItemsCollection();
 //Get current product trying to be added
 $product = Mage::getModel('catalog/product')
 - > load(Mage::app() - > getRequest() - > getParam('product', 0));
 /*
 * Your code logic to see restricted items in cart
 * 
 */
 $isRestricted = $this - > hasRestrictedItems($quoteItem, $product);
 if ($isRestricted) {
 Mage::getSingleton("core/session") - > addError("You can not add this product");
 return;
 }
 }
}

Make sure you implement your restricted products logic in hasRestrictedItems().

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