php var_dump($object) or print_r($object) to a log file

Question

This question is generic, and I would simply like to know how to dump objects to log files. In order to clarify things, i am elaborating through an example.

I have been successfully using magento observers to call methods when certain events happen. As an example, I am observing for when a shipment is saved via :

<sales_order_shipment_save_after>

and i'm successfully calling a method. I would like to grab the shipment and simply dump the object to a log file. eg.

public function newShipment(Varien_Event_Observer $observer)
{
    $shipment = $observer->getEvent()->getShipment();
    $shipId = $shipment->getId();
    Mage::log("shipment ({$shipId}) created/saved", null, 'shipments.log');
    //trying to dump $shipment data into the log file
    Mage::log("({var_dump($shipment)}) ------", null, 'shipments.log');
    Mage::log("----------------------------", null, 'shipments.log');
}

The shipment id is printed into the log file just fine, but obviously it does not dump the object the way i want it to as the code I have written is wrong.

Can anyone tell me how I could dump an object to a log file and perhaps give me some advice on logging in general?

thanks very much.

Answer 1

Mage::log(
    $object->debug(), //Objects extending Varien_Object can use this
    Zend_Log::DEBUG,  //Log level
    'my.log',         //Log file name; if blank, will use config value (system.log by default)
    true              //force logging regardless of config setting
);

Answer 2

To be able to use Mage::log(), some conditions need to be met:

• developer mode must be set to true
• logging must be activated in the system configuration.

But, you can also force logging by passing true as 4th param to Mage::log().

If all conditions are met (or logging is forced), you should find your log file in var/log/shipping.log.

As a side note: Magento objects tend to be huge and usually contain tons of informations that you usually don't really need for logging/debugging purposes.

You can reduce the amount of dumped information by using the getData() method, a member of all Magento objects extending Varien_Object:

Mage::log(print_r($shipment->getData(), true), null, 'shipment.log', true);

You can also dump single attributes by using its proper getter method:

Mage::log((string) $shipment->getId(), null, 'shipment.log', true);

If you really need full object dumps, I'd recommend to use the debug() method of the object to log the data (this method autodetects recursions which helps avoiding endless loops eating up all memory):

Mage::log($shipment->debug(), null, 'shipment.log', true);

If you can't get Mage::log() to work, you alternatively could use PHP's core error_log function to log. That's what I sometimes do, if I need just a quick log.

error_log(print_r($shipment->getData(), true), 3, 'shipment.log');