How will you join flat table and EAV table in Magento?

Joining tables in Magento when it comes to EAV with Flat table is quite complicated. Consider you want to join sales_flat_order table with customer EAV tables to get Customer’s firstname and lastname, it becomes difficult as customer’s name comes from customer_entity_varchar table.

Below code will join sales order flat table with customer EAV to get customer’s full name in the collection along with all the order details.
 

$coll = Mage::getModel('sales/order')->getCollection();

$fn = Mage::getModel('eav/entity_attribute')->loadByCode('1', 'firstname');
$ln = Mage::getModel('eav/entity_attribute')->loadByCode('1', 'lastname');

$coll->getSelect()
    ->join(array('ce1' => 'customer_entity_varchar'), 'ce1.entity_id=main_table.customer_id', array('firstname' => 'value'))
    ->where('ce1.attribute_id='.$fn->getAttributeId())
    ->join(array('ce2' => 'customer_entity_varchar'), 'ce2.entity_id=main_table.customer_id', array('lastname' => 'value'))
    ->where('ce2.attribute_id='.$ln->getAttributeId())
    ->columns(new Zend_Db_Expr("CONCAT(`ce1`.`value`, ' ',`ce2`.`value`) AS fullname"));

print_r($coll->getData());