magento add last login to customer grid - magento

Question

I am new to Magento. I am trying to add a last login value displaying on customer grid. it returns a null value. I have read other tutorials, but it does not help much. The Magento version is 1.7. Here is my code:
$customer = Mage::getSingleton('customer/session')->getCustomer();
$logCustomer = Mage::getModel('log/customer')->load($customer ->getId());
$lastVisited = $logCustomer->getLoginAt();
$this->addColumn('$lastVisited', array(
'header' => Mage::helper('customer')->__('Last Login'),
'type' => 'datetime',
'align' => 'center',
'index' => '$lastVisited',
'gmtoffset' => true
));

Answer 1

Magento stores the login time in the following table:
log_customer
But also, this data is cleaned periodically (see: Mage_Log_Model_Resource_Log::_cleanCustomers which is triggered via Magento cron).
There are different ways to approach your task.
1) Non-persistent - I am just interested to see recent data (I can ignore that log_customer is cleaned periodically)
In this case you can just rely on the data from log_customer and display it in Manage Customers Grid.
Extend Mage_Adminhtml_Block_Customer_Grid and in _prepareCollection add the following:
$collection->getSelect()->columns(array('last_login_at' => new Zend_Db_Expr ("(SELECT login_at
FROM `log_customer`
WHERE customer_id =e.entity_id
ORDER BY log_id DESC
LIMIT 1)")));
before: $this->setCollection($collection);
Note: use the proper Magento function to get log_customer table name, my query is just for example
2) Persistent - I want to always to see the data
add a new attribute to the customer entity called: last_login_at
(datetime).
add an observer to custom_login event to update this
attribute.
use addColumn function in the grid to display this new attribute.
#user1414056
Regarding your code:
bixe made a fair point related to '$lastVisited' (this just shows
lack of experience in php programming
you seem to also be new to programming (in general) because the addColumn is called only once... do how do you expect your code to make sense?
With a better understanding of Zend Framework and OOP Programming in general you will be able to actually work and get things done with Magento.

Answer 2

Your '$lastVisited' can't work : in php variables are evaluated in a String only when they're in a double quote.
EDIT:
Ok the column system of magento only display value when they're available in the collection linked to the grid..
You'll have to add the log information you want to display in the grid collection.
For an example, take a look at Mage_Adminhtml_Block_Customer_Online_Grid::_prepareCollection()
When it's done, you will add your column with :
$this->addColumn('login_at', array(
'header' => Mage::helper('customer')->__('Last Login'),
'type' => 'datetime',
'align' => 'center',
'index' => 'login_at',
'gmtoffset' => true
));