Magento – How is the array $data parameter set in Magento 2 (dataObject constructor)

dependency-injectionmagento2object-manager

In https://github.com/SnowdogApps/magento2-menu/blob/master/Block/Menu.php, a plugin that makes it possible to replace the default menu, the constructor of the block looks like below.

For all arguments / parameters in the constructor except array $data, my understanding is that those are somehow managed through the object manager and created if not existing. However, I'm stuck at figuring out how the array $data is set. In https://github.com/SnowdogApps/magento2-menu/blob/master/etc/di.xml, there is no argument named data.

Menu.php constructor:

public function __construct(
    Template\Context $context,
    EventManager $eventManager,
    MenuRepositoryInterface $menuRepository,
    NodeRepositoryInterface $nodeRepository,
    NodeTypeProvider $nodeTypeProvider,
    SearchCriteriaFactory $searchCriteriaFactory,
    FilterGroupBuilder $filterGroupBuilder,
    array $data = []
) {
    parent::__construct($context, $data);
    $this->menuRepository = $menuRepository;
    $this->nodeRepository = $nodeRepository;
    $this->nodeTypeProvider = $nodeTypeProvider;
    $this->searchCriteriaFactory = $searchCriteriaFactory;
    $this->filterGroupBuilder = $filterGroupBuilder;
    $this->eventManager = $eventManager;
}

I've looked on this related question (Magento 2: what is the $data array constructor parameter?) and went to myMagentoRootFolder/vendor/magento/framework/DataObject.php, to have a look on the class which is inherited and uses the $data-parameter, this didn't make me understand it. Furthermore, I don't that the default empty array would work, because the getData()-method is used by the module and an empty response would be of no use.

DataObject.php constructor:

/**
 * Constructor
 *
 * By default is looking for first argument as array and assigns it as object attributes
 * This behavior may change in child classes
 *
 * @param array $data
 */
public function __construct(array $data = [])
{
    $this->_data = $data;
}

*Menu.php extends Template, and Template extends AbstractBlock, and AbstractBlock extends DataObject

So, I don't understand how and where array $data is set. Any help is appreciated, as I've been struggling to understand this for some days.

Best Answer

Data is set when instantiating the object, either through factory(preferred) or through object manager.

Factory:

$this->factory->create(['data' => ['key' => 'value']]);

Object Manager:

$this->_objectManager->create(\Class, ['data' => ['key' => 'value']]);

Data can be set after instantiating the object by using setData

Related Solutions

Magento 2 – Dependency Injection Constructor Arguments

I haven't actually tracked this down through code, but here's how I've come to reason about it, and the behavior described below appears to be true (even if the behind the scenes code used by the object manager is different). That said, your question leaves some important details out and is a little vague -- see comments below for some requested clarification that might clear things up.

When the object manager instantiates an object, it looks at your class's __construct method. If your class doesn't have a __construct method, then it looks at the next class's __construct method, etc. until it finds a class with a __construct. Once found, it uses those constructor parameters, and those paramaters only, to build a list of parameters to inject.

Put another way, the object manager will inject the parameters in the constructor PHP would normally call. Remember, PHP only calls one constructor. If you want a parent's constructor class to be called, you need to do parent::__construct(...). This means if the parent class needs a specific list of parameters, its your job to ensure they're also injected in your constructor (so that you can pass them on with parent::__construct).

Regarding your specific questions

Now for learning purposes i did this to see with is being injected (it doesn't take more then two arguments by default).

Your testing methodology seems like it might be a problem here. I tried creating a __construct method in a custom frontend controller that looked like this

public function __construct($a, $b)
{
    var_dump(get_class($a));
    var_dump(get_class($b));
}

And Magento/PHP yelled at me

Missing required argument $a of Pulsestorm\Commercebug\Controller\Lookup\Index

It's also unclear from your questions if these were frontend or backend controllers. If you include more specific code and expand on the steps you used to create your controller, someone may be able to help you understand why the constructor receives a Context object and a page factory object

Regarding the Magento\Sales\Controller\Adminhtml\Order\AbstractMassAction class: If your class extends this class, Magento will inject what parameters are in your __construct method. If your class doesn't have a __construct method, they you don't need to worry about what's injected. Magento will handle it for you via the parent class.

Magento 2 – Understanding the $data Array Constructor Parameter

The $data can be used to populate data on your object since the constructor of \Magento\Framework\DataObject is this

public function __construct(array $data = [])
{
    $this->_data = $data;
}

or similar for Magento\Framework\Api\AbstractSimpleObject

/**
 * Initialize internal storage
 *
 * @param array $data
 */
public function __construct(array $data = [])
{
    $this->_data = $data;
}

which a lot of classes in Magento extend from.

A common use is in conjunction with a factory. For example in Magento\Sales\Model\Order\CustomerManagement we have:

$this->addressFactory->create(['data' => $addressData]);

which essentially populates the $data array at creation.

Having to keep the $data = [] at the end of the list of parameters is normal php behaviour since you are assigning a default value - the empty array.

Best Answer

Related Solutions

Magento 2 – Dependency Injection Constructor Arguments

Magento 2 – Understanding the $data Array Constructor Parameter

Related Topic