Extending Magento Shopping Cart

Question

I need to extend the Magento shopping cart to include an extra step for a store locator. I understand that I need to overwrite the core OnePage controller (Mage_Checkout_OnepageController) and blocks (Mage_Checkout_Block_Onepage) but what needs to be done with regards to keeping track of the extra information (e.g. user's selected options from my custom step).

Answer 1

There are a number of steps required here to get the whole solution.

Firstly, create a new module. Use the ModuleCreator if you wish.

Then, write a setup script in your module to add the new fields to Magento's attribute structure, e.g. :

 $setup = new Mage_Sales_Model_Mysql4_Setup('core_setup');
 $setup->startSetup();

 $setup->addAttribute('quote', 'my_attribute', array('type' => 'varchar', 'visible' => false, 'required' => false));
 $setup->addAttribute('order', 'my_attribute', array('type' => 'varchar', 'visible' => false, 'required' => false));
 $setup->addAttribute('invoice', 'my_attribute', array('type' => 'varchar', 'visible' => false, 'required' => false));
$setup->addAttribute('creditmemo', 'my_attribute', array('type' => 'varchar', 'visible' => false, 'required' => false));

Note the use of the Mage_Sales_Model_Mysql4_Setup to add the fields to the relevant sales_flat_quote and sales_flat_order tables.

Now, insert the following values in your module's config.xml file:

<global>

    <fieldsets>
        <sales_convert_quote>
            <my_attribute>
                <to_order>*</to_order>
            </my_attribute>
        </sales_convert_quote>
        <sales_convert_order>
            <my_attribute>
                <to_cm>*</to_cm>
                <to_invoice>*</to_invoice>
            </my_attribute>
        </sales_convert_order>
    </fieldsets>

That will instruct Magento to copy the values of your custom field from quote to order to invoice and credit_memo, etc.

Then in your custom block/controller code, you will be able to use Magento's magic getters and setters to persist the values.

$oQuote = Mage::getSingleton('checkout/session')->getQuote();
$oQuote->setMyAttribute('some_value');
$oQuote->save();

You should see the new column and value saved in sales_flat_quote. Then once the customer completes checkout, the same value should be saved in sales_flat_order.

Note that the above code can be extended to work for quote_item and order_item by just changing quote to quote_item etc, however, if you wish to save attribute values that have been set on your products, then some extra work is required.

Insert a new block of XML into your config.xml (again inside the global node):

   <sales>
        <quote>
            <item>
                <product_attributes>
                    <my_attribute />
                </product_attributes>
            </item>
        </quote>
    </sales>

Where my_attribute is the attribute code on the product model. That will make the my_attribute available on the linked product, so you can access it via

$oQuoteItem->getProduct()->getMyAttribute()

without needing to perform a full Mage::getModel('catalog/product')->load($oQuoteItem->getProductId()). This is much more efficient.

Then, you will need an observer to copy the values from the product object to the quote_item object. So, declare your observer in the config.xml:

    <events>
        <sales_quote_item_set_product>
            <observers>
                <quoteitem_set_custom_data>
                    <type>singleton</type>
                    <class>mymodule/observer</class>
                    <method>setCustomDataOnQuoteItem</method>
                </quoteitem_set_custom_data>
            </observers>
        </sales_quote_item_set_product>
    <events>

and write code in your observer class like this:

public function setCustomDataOnQuoteItem($oObserver){
    $oProduct = $oObserver->getProduct();
    $oQuoteItem = $oObserver->getQuoteItem();
    foreach(array('my_attribute') as $vAttributeCode){
        $oQuoteItem->setData($vAttributeCode,$oProduct->getData($vAttributeCode));
    }
}