In Magento 2, they introduced the usage of dependency injection, which is a well-known design pattern that changes the way you use resources in the code. Using dependency injection, all the required resources are created when the class is instantiated instead of creating an object (through the Magento 1.x Mage class) when necessary. The benefit of this is that it is easier to use unit testing as it is possible to mock the required objects.
In this example, we will see how to create a new record in the demolist model created in the previous chapter. The record is created using an observer on the sales_order_place_after event that is dispatched after a new order is saved.