Magento : Update Cart Grand Total and Subtotal

Question

I have 4 main products in cart, Each item is having different price. I want to update cart's total price as $40 without considering each line item price. I want to show $40 as combined price for all 4 items.

I tried with below code, but this can update each line item price.

<events>            
   <sales_quote_add_item>
       <observers>
          <Company_Module_Model_Observer>
             <type>singleton</type>
             <class>Company_Module_Model_Observer</class>
             <method>updatePrice</method>
          </Company_Module_Model_Observer>
      </observers>
   </sales_quote_add_item>
</events>

  <?php
  class Company_Module_Model_Observer
  {
      public function getNewPrice()
      {
          $quote = Mage::getSingleton('checkout/session')->getQuote();
          $cartItems = $quote->getAllVisibleItems();

          $custom_price = 40;

          foreach ($cartItems as $item) {
              $productId = $item->getProductId();
              $product = Mage::getModel('catalog/product')->load($productId);

              $actualPrice = $product->getPrice();

              $newprice = $custom_price;            
          }

          return $newprice;
      }

      public function updatePrice($observer)
      {
          $event = $observer->getEvent();
          $product = $event->getProduct();
          $quote_item = $event->getQuoteItem();
          $new_price = $this->getNewPrice();
          $quote_item->setOriginalCustomPrice($new_price);
          //$quote_item->save();
          $quote_item->getQuote()->save();
          //Mage::getSingleton('checkout/cart')->save();
      }

  }

Answer 1

Please reconsider your logic. From a customer point of view, it is not a best practice to display a Grand Total value other than the total price of items in cart.

Or you can use the Bundle Item products feature, where you can configure multiple products with different price value under a single bundle product and set the price value of bundle product to be fixed.

If my understanding is wrong, on your query, please give a more clear picture what you are trying to achieve.

Answer 2

Kindly find below URL for showing custom total.

URL :http://magento.ikantam.com/qa/how-add-discount-total-magento

public function collect(Mage_Sales_Model_Quote_Address $address) {
            if ($address->getData('address_type') == 'billing')
                return $this;

                $discount = Mage::helper('my_module')->getCurrentdiscount(); // Custom percentage

                $grandTotal = $address->getGrandTotal();
                $baseGrandTotal = $address->getBaseGrandTotal();

                $totals = array_sum($address->getAllTotalAmounts());
                $baseTotals = array_sum($address->getAllBaseTotalAmounts());

                $address->setFeeAmount(-$totals * $discount / 100);
                $address->setBaseFeeAmount(-$baseTotals * $discount / 100);

                $address->setGrandTotal($grandTotal + $address->getFeeAmount());
                $address->setBaseGrandTotal($baseGrandTotal + $address->getBaseFeeAmount());
        return $this;
    }