Magento2 ObjectManager preferences

Mar 14, 2016 Magento

When developing with Magento2 you have maybe come to the question were is my logger for example. This was the way in Magento before.

Mage::log('Some log message', null, 'file.log');

Maybe you have already found the logger here for example in the class Magento\Backup\Controller\Adminhtml\Index\Rollback.

$this->_objectManager->get('Psr\Log\LoggerInterface')->info($e->getMessage());

Today I don't want to show you the logger. More interesting for me are the shared instances inside of the Objectmanager that you can use with the fucntion get.

The general object manager can be found in this class Magento\Framework\ObjectManager\ObjectManager and it implements the interface \Magento\Framework\ObjectManagerInterface. Here you see the get function.

/**
 * Retrieve cached object instance
 *
 * @param string $type
 * @return mixed
 */
public function get($type)
{
    $type = ltrim($type, '\\');
    $type = $this->_config->getPreference($type);
    if (!isset($this->_sharedInstances[$type])) {
        $this->_sharedInstances[$type] = $this->_factory->create($type);
    }
    return $this->_sharedInstances[$type];
}

Adding a shared instance

You can add your own shared instance with the preference tag in your etc/di.xml. For example here a snipped of magento/module-backend/etc/di.xml.

<?xml version="1.0"?>
<!--
/**
 * Copyright © 2015 Magento. All rights reserved.
 * See COPYING.txt for license details.
 */
-->
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <!-- ... -->
    <preference for="Magento\Framework\App\Config\Storage\WriterInterface" type="Magento\Framework\App\Config\Storage\Writer" />
    <!-- ... -->
</config>

A list of shared instances

Here is a default list of shared instances that you can use with the get function.