On the other hand, admin should be able to view the comment on the order page.

Adding a custom comment box for each item in the cart is actually very easy. First lets add the textarea field for each item.

In your theme, for the file: template/checkout/cart.phtml
Add the new heading along with other heading for cart items.

<th><?php echo $this->__('Comments') ?></th> 

In the file: template/checkout/cart/item/default.phtml
Add a new column

            <td class="a-center">
            <textarea name="cart[<?php echo $_item->getId() ?>][comments]" rows="3" cols="20"><?php echo $_item->getItemcomment() ?></textarea>
            </td>

For Older version of Magento it would be:

            <td class="a-center">
            <textarea name="cart[<?php echo $_item->getId() ?>][comments]" rows="3" cols="20"><?php echo $this->getItemItemcomment($_item) ?></textarea>
            </td>

Doing upto this. shoul show the text area added

The next step is to save the comment in DB, when customer update the cart.

So add a new field ‘itemcomment’ in the tabel ‘sales_flat_quote_item’. (For older version of Magento the table would be ‘sales_quote_item’)

Now we are going to add the code which will do the DB operation. For this we will need to modify the file:
app/code/core/Mage/Checkout/Model/Cart.php (Note: If you are planning to upgrade your Magento setup, copy this file to local & modify.)

Here we need to add some code to the function updateItems(), such a way that the function should now look like below:

    public function updateItems($data)
    {
        Mage::dispatchEvent('checkout_cart_update_items_before', array('cart'=>$this, 'info'=>$data));

        foreach ($data as $itemId => $itemInfo) {

            $item = $this->getQuote()->getItemById($itemId);
            if (!$item) {
                continue;
            }

            if (!empty($itemInfo['remove']) || (isset($itemInfo['qty']) && $itemInfo['qty']=='0')) {
                $this->removeItem($itemId);
                continue;
            }

            $qty = isset($itemInfo['qty']) ? (float) $itemInfo['qty'] : false;
            if ($qty > 0) {
                $item->setQty($qty);
            }

        /* Start: Custom code added for comments */
        if(!empty($itemInfo['comments'])) {

        	$write = Mage::getSingleton('core/resource')->getConnection('core_write');

        	# make the frame_queue active
      		$query = "UPDATE `sales_flat_quote_item` SET itemcomment = '".$itemInfo['comments']."' where item_id = $itemId";
			$write->query($query);

        	$item->setItemcomment($itemInfo['comments']);
        }
        /* End: Custom code added for comments */

        }

        Mage::dispatchEvent('checkout_cart_update_items_after', array('cart'=>$this, 'info'=>$data));
        return $this;
    }

Showing the comment in Admin -> View Order

Add a new function getItemcomment() to the file below:
app/code/core/Mage/Adminhtml/Block/Sales/Order/View/Items.php

If you are on verstion 1.5 or later.. add it to the file below.
app/code/core/Mage/Adminhtml/Block/Sales/Order/View/Items.php

	public function getItemcomment($item) {
		$itemId = $item->getId();

		$write = Mage::getSingleton('core/resource')->getConnection('core_write');

    	$query = "SELECT q.* FROM `sales_flat_order_item` o
	    LEFT JOIN `sales_flat_quote_item` q on o.quote_item_id = q.item_id
	    WHERE o.item_id = $itemId";

		# For older versions of Magento
/*	    $query = "SELECT q.* FROM `sales_order_entity_int` o
	    LEFT JOIN `sales_flat_quote_item` q on o.value = q.entity_id
	    WHERE o.entity_id = $itemId AND o.attribute_id = 343";       */	    

		$res = $write->query($query);

		while ($row = $res->fetch() ) {
			if(key_exists('itemcomment',$row)) {
				echo nl2br($row['itemcomment']);
			}
		}
	}    

To add the comments column to the items edit the .phtml file below:
app/design/adminhtml/default/default/template/sales/order/view/items.phtml

Adding header for items to make it look like below:

.
.
<tr class="headings">
    <th><?php echo $this->helper('sales')->__('Product') ?></th>
    <th><?php echo $this->helper('sales')->__('Comments') ?></th>
    <th><?php echo $this->helper('sales')->__('Item Status') ?></th>
.
.
.

Adding Column with comments. app/design/adminhtml/default/default/template/sales/order/view/items/renderer/default.phtml
Add a column for item comments juts before status columns to make it look a like below.

.
.
<td><?php echo $this->getItemcomment($_item) ?></td> <!-- New column added for item comments -->
<td class="a-center"><?php echo $_item->getStatus() ?></td>
.
.

Doing upto this will show the comments column in the item table. It should look like image below.

As a solution, I replaced the version of file below from Magento 1.4.0 to Magento 1.4.1

js/prototype/validation.js

Also disabled the Centinel Validation by commenting the line below in file : app/code/core/Mage/Payment/Model/Method/Cc.php

this->getCentinelValidator()->validate($this->getCentinelValidationData());

The data on the cart page is coming from the table ‘sales_flat_quote_item’. This table is having lot many fields. Some of them are product_id, name, description, qty, price. Those are the fields which basically reflects on the cart page.

My task was to display the custom image, custom price, custom description in the row of a product on the cart page.

So first of all we need to insert those values in the DB, while adding the product to the cart.

The phase of adding the product to cart is bit complicated to understand.

These are list of some functions involved in Add to cart phase.

app/code/core/Mage/Checkout/controllers/CartController.php: addAction()
app/code/core/Mage/Checkout/Model/Cart.php: addProduct($product, $info)
app/code/core/Mage/Sales/Model/Quote.php: addProduct(Mage_Catalog_Model_Product $product, $request=null)

In the above function, you can set the custom values for the product.

Find the for loop:
foreach ($cartCandidates as $candidate) { … }
Inside that custom fields can be set.

foreach ($cartCandidates as $candidate) {
            $item = $this->_addCatalogProduct($candidate, $candidate->getCartQty());
            ...
            ...
            ...
            $item->setCustomPrice('custom value goes here');
            $item->setCustomImage('custom value goes here');
            ...
            ...
}

I want the custom image as well. So I have added the one more field in the table ‘sales_flat_quote_item’.

Getting those custom values on the cart page is very easy. Go to template/checkout/cart/item/default.phtml.
The below lines can get those values.

echo $_item->getCustomImage();

The price on the cart page will replaced automatically by custom_price value if that has been set.