To use or not to use the ObjectManager directly?

Question

Ok, so yesterday we had a big talk with other people from the Magento community regarding the direct use of the ObjectManager in classes/templates.

I'm already aware of the reasons why we shouldn't use the ObjectManager directly, quoting Alan Kent :

There are several reasons. The code will work, but it is best practice to not reference the ObjectManager class directly.

• Because we say so! ;-) (better expressed as consistent code is good code)
• The code could be used with a different dependency injection framework in the future
• Testing is easier - you pass in mock arguments for the required class, without having to provide a mock ObjectManager
• It keeps dependencies clearer - it is obvious what the code depends on via constructor list, rather than having dependencies hidden in the middle of the code
• It encourages programmers to think about concepts like encapsulation and modularization better - if the constructor gets big, maybe it is a sign the code needs refactoring

From what I've seen in StackExchange, a lot of people tend to go for the easy/short/not recommended solution for example something like this:

<?php 
//Get Object Manager Instance
$objectManager = \Magento\Framework\App\ObjectManager::getInstance();

//Load product by product id
$product = $objectManager->create('Magento\Catalog\Model\Product')->load($id);

Instead of going through the painful but recommended process of:

• creating a module
• declaring preferences
• inject dependencies
• declare a public method

However, and here comes the dilemma, Magento 2 core files often call the ObjectManager directly. A quick example can be found here: https://github.com/magento/magento2/blob/develop/app/code/Magento/GoogleOptimizer/Block/Adminhtml/Form.php#L57

So here are my questions:

• Why is Magento doing what they recommend us not to do ? Does that mean there are some cases where we should use the ObjectManager directly? If so, what are those cases?
• What are the consequences of using the ObjectManager directly?

Answer 1

You should not use the ObjectManager directly!

Exception from the rule are:

• in static magic methods like __wakeup, serialize, etc
• in case you should make backward compatibility of constructor
• in global scope, like in fixtures of integration test.
• in class that needs only for creation of object like factory, proxy , etc

Answer 2

So why does M2 sometimes access object manager directly when we recommend against it?

Brutal answer: M2 is a port of M1 - not a complete rewrite. So don't assume that all the M2 code is perfectly ported yet (unfortunately). Just because you find something in the M2 code base, that does not mean "its the best way to do it". Sometimes it is just "we have not got around to fixing it yet".

Less brutal: As per other responses, sometimes you MUST use it as there is no alternative. Other times it might be for backwards compatibility reasons. And framework code sometimes makes sense using it directly, because it is framework code. But if I had to guess without looking at code, many really should be fixed but it has not been high enough priority to do so yet.

Just remember the good parenting advice: "Kids, do what I say, not what I do!"

Answer 3

You should never use \Magento\Framework\App\ObjectManager::getInstance().
It defeats the purpose of dependency injection. We're back at Mage::getModel().
Object manager should be used only in factories and then as injected in a constructor.

The advantage of using this is less code to write. But this does not make it OK.
The fact that this is still used in the core, is because it didn't get refactored yet. I hope it will be.

Answer 4

Why is Magento doing what they recommend us not to do ? Does that mean there are some cases where we should use the ObjectManager directly ? If so, what those cases ?

Without knowing the full story here is my guess:

During the development of M2 the Magento team at some stage ran an automated script which replaced occurrences of Mage:getModel(), Mage::getSingleton(), $layout->createBlock(), etc. to use the ObjectManager.

Later refactoring should have fixed this to instead use proper dependency injection but there wasn't enough time / resources to convert all occurrences.

Also the Magento team lately seems to use this as an escape mechanism. Instead of breaking an existing implementation (by needing to change the constructor) they simply hide the new dependency via the ObjectManager. I can't say I agree with this approach - writing worse code to avoid a BC break.

What are the direct consequences of using the ObjectManager directly ?

I think your question already includes enough reasons. Generally it creates a hidden dependency, in other words the dependency is in the implementation details and not visible from the constructor alone.

Answer 5

Should not use Object manager directly!

For instance:

\Magento\Framework\App\ObjectManager::getInstance();

also if you are working with event observers or plugins, you should never use it directly.

You could use it in Factories, but except that you should inject the Object Manager in the Constructor first then you can use its object in your method

Preferred to use:

1) declare private object:

private $_objectManager;

2) inject in the constructor and initialize:

public function __construct(
    \Magento\Framework\ObjectManagerInterface $objectmanager
) {
    $this->_objectManager = $objectmanager;
}

3) use in some method:

public function create() {
    return $this->_objectManager->create(/* ......... */);
}

This answer is for below Magento 2.2 versions, so please take a note. As per new Magento 2 standards now we can not use even objectManager instance, too. We have to use factory of the object class or repository to get any data.

Answer 6

The main reason that developers are strongly discouraged from using the Object Manager directly is that direct use of the Object Manager causes the extension not to be installable in compiled release mode.

So it breaks for your customers using release mode, including all customers on Magento Cloud.

It seems like a reasonably large proportion of developers (approximately 75%) do not test their extensions to see if they can be installed in release mode, so do not run into the issues posed by incorrect ObjectManager usage.

As of 2017, the Magento Marketplace runs a compile and install test on all extensions sold through it. If your extension uses the Object Manager directly, it will fail these tests and be rejected from the Marketplace until you resolve this problem and reupload.

Answer 7

You can try by creating an object of objectManager and should not use objectManager directly.

Use something like,

class Example extends \Magento\Framework\View\Element\Template
{
    private $_objectManager;

    public function __construct(
        \Magento\Framework\ObjectManagerInterface $objectmanager
    ){
        $this->_objectManager = $objectmanager;
    }

    public function getExample()
    {
        $customerSession = $this->_objectManager->create("Magento\Customer\Model\Session");
        if ($customerSession->isLoggedIn()) {
            $customerData = $customerSession->getCustomer()->getData();
            /*Your logic*/
        }
    }
}

Answer 8

You should not call the object manager directly because the framework handles this automatically. You can see few exceptions that Magento 2 core classes call the ObjectManager directly because this code needs exist for backward compatibility purposes. But, they are not approval of using the ObjectManager directly.

Moreover, if you run:

bin/magento dev:di:info "Magento\Quote\Model\QuoteRepository"

you will get "information on Dependency Injection configuration", but you will not get the information of direct usage of ObjectManager. Also, direct use of its create() function prevents type validation and type hinting that a factory class provides.

Answer 9

You can use below code for get all category and sub category Data like category id, name, url and etc.

$objectManager = \Magento\Framework\App\ObjectManager::getInstance();
$storeManager = $objectManager->Create('\Magento\Store\Model\StoreRepository');    
    $categories = $objectManager->Create('\Magento\Catalog\Model\ResourceModel\Category\Collection')
                   ->addAttributeToSelect('*')
                   ->addAttributeToSort('path', 'asc');

    foreach($categories as $category){
        echo $category->getId().'--'.$category->getName();

And for more detail click here.