You will need to have basic knowledge of PHP, OOP, JavaScript, and XML. You will also need Apache, MySQL, and AMPPS installed on your system to execute the codes.

The code files of this chapter can be found on GitHub:
https://github.com/PacktPublishing/Magento-2-Quick-Start-Guide.

Check out the following video to see the Code in Action:

http://bit.ly/2PKYvUx.

There are two types of persistence models in Magento: simple and Entity–attribute–value (EAV). The term entity is tossed around interchangeably between the two types of models. We can think of an entity as any persistable model.

The Subscriber entity of the Magento_Newsletter module is an example of a simple model. We can see that it's comprised of the following:

• A model of type Magento\Newsletter\Model\Subscriber extends Magento\Framework\Model\AbstractModel
• A resource model of type Magento\Newsletter\Model\ResourceModel\Subscriber extends Magento\Framework\Model\ResourceModel\Db\AbstractDb
• A collection of type Magento\Newsletter\Model\ResourceModel\Subscriber\Collection extends Magento\Framework\Model\ResourceModel\Db\Collection\AbstractCollection

The Customer entity of the Magento_Customer module is an example of an EAV model...

Every time a module is installed via a php bin/magento module:enable command, Magento shows the following message: To make sure that the enabled modules are properly registered, run 'setup:upgrade'. The php bin/magento setup:upgrade command upgrades the Magento application, database data, and schema. Once triggered, the upgrade command instantiates Magento\Setup\Model\Installer, which then goes through a series of methods. Its getSchemaDataHandler method reveals the types of available setup scripts:

• InstallSchema.php
• UpgradeSchema.php
• Recurring.php
• InstallData.php
• UpgradeData.php
• RecurringData.php

These scripts live under the <VendorName>/<ModuleName>/Setup directory.

Once successfully finished, the setup:upgrade command makes a new entry, or updates an existing one, in the setup_module table. There, we can see the schema_version...

We extend entities by adding additional attributes to them. Referring back to the magical getter and setter methods mentioned in the context of Magento\Framework\DataObject, the logical thinking might be: what's the big deal; can't we just add new database columns via UpgradeSchema and use magical getter and setter methods to go around it? The answer is both yes and no, but mainly leaning toward no – we will soon learn why.

To better explain this, let's take a look at Magento\Sales\Model\Order, the entity model. This model implements the Magento\Sales\Api\Data\OrderInterface interface, which further extends Magento\Framework\Api\ExtensibleDataInterface. Here, we can see a constant defining a key for the extension attributes object. This is somewhat of a starting point for extending entities. Suffice to say, there is an extra abstraction...

Throughout this chapter, we learned how to differentiate the three types of Magento models: non-persistable, persistable simple, and persistable EAV. The inners of EAV models are left out of scope due to their inherently complex nature. We then took a look through six different setup scripts. These give us a great deal of flexibility over schema and data management. Combined with extension attributes, we get a powerful mechanism for extending built-in entities. Though somewhat tedious, the extension attributes mechanism use of interfaces ensures that integrators can extend this built-in functionality with complex data types.

Moving forward, we are going to take a look at the powerful web API that's implemented in Magento.