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Magento WordPress (MWI) Session Error Fix

Here at Cadence Labs, we’ve done a number of Magento-WordPress integrations using the MWI plugin (see our full article here: https://www.cadence-labs.com/2015/02/use-magento-theme-wordpress/ ). One error we run into with more complex builds is:

PHP Fatal error: Mage_Core_Model_Session_Abstract::getMessages() [mage-core-model-session-abstract.getmessages]: The script tried to execute a method or access a property of an incomplete object. Please ensure that the class definition “Mage_Core_Model_Message_Collection” of the object you are trying to operate on was loaded _before_ unserialize() gets called or provide a __autoload() function to load the class definition in {magento_path}/app/code/core/Mage/Core/Model/Session/Abstract.php on line 215

What’s happening is that WordPress is loading the core message session information before the class definition for Mage_Core_Model_Message_Collection has been defined. What we need to do is tell Magento to ignore the core message queue if we’re running inside a WordPress page/post.

The Fix

Create a local copy of Mage_Core_Model_Session_Abstract:

mkdir -p app/code/local/Mage/Core/Model/Session
cp app/code/core/Mage/Core/Model/Session/Abstract.php app/code/local/Mage/Core/Model/Session/Abstract.php

In our new local copy, we’re going to modify the function getMessages() to look like the below:

     * Retrieve messages from session
     * @param   bool $clear
     * @return  Mage_Core_Model_Message_Collection
    public function getMessages($clear=false)
        if (isset($_SERVER['REQUEST_URI']) && strstr($_SERVER['REQUEST_URI'], '/YOUR_WORDPRESS_PATH')) {
            return Mage::getModel("core/message_collection");
        if (!$this->getData('messages')) {

        if ($clear) {
            $messages = clone $this->getData('messages');
            return $messages;
        return $this->getData('messages');

You can see, what we’re doing is telling Magento to not attempt a read from the Session (for core messages only) in the event we’re on a wordpress page.

Change /YOUR_WORDRESS_PATH to the subdirectory where WordPress is installed.

** Author’s note: If you are running Magento in a subdirectory (WordPress in the base) you’ll need to create a Magento module to make this work. We currently don’t have the tutorial online yet, but hope to provide it in the coming days.

Alan Barber is the Lead Web Developer at Cadence Labs and a Magento Certified developer.

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