Using object manager

Dependency injection

If you wanted to load an order object using the order repository via the ObjectManager you would do something like:

$objectManager = \Magento\Framework\App\ObjectManager::getInstance();
$orderRepository = $objectManager->get(\Magento\Sales\Api\OrderRepositoryInterface::class);
try {
    // Load order with entity_id 1
    $order = $orderRepository->get(1);
} catch (\Exception $e) {
    // Order not found
}
// Do something with order object

However you should inject the OrderRepositoryInterface using constructor dependency injection like so:

private OrderRepositoryInterface $orderRepository;

public function __construct(
    \Magento\Sales\Api\OrderRepositoryInterface $orderRepository
) {
    $this->orderRepository = orderRepository;
)

public function someFunction()
{
    try {
        $order = $this->orderRepository->get(1);
    } catch (\Exception $e) {
        // Order not loaded
    }
    // Do something with order object
}

There are several reasons you should do this:

• Enables you to write testable code, allowing you to pass mock objects into your class to run test cases with,
• It is also cleaner using DI as you do not need to get instances of the class yourself,
• It allows you to use Magento's di.xml to replace dependancies as required, for example a different areacode such as webapi_rest or frontend may benefit from a different class being injected in.