Service contracts

A service contract is a set of PHP interfaces that is defined by a module. This contract comprises data interfaces and service interfaces.

The role of the data interface is to preserve data integrity, while the role of the service interface is to hide the business logic details from service consumers.

Data interfaces define various functions, such as validation, entity information, search related functions, and so on. They are defined within the Api/Data directory of an individual module. To better understand the actual meaning of it, let's take a look at the data interfaces for the Magento_Cms module. In the vendor/magento/module-cms/Api/Data/ directory, there are four interfaces defined, as follows:

BlockInterface.php
BlockSearchResultsInterface.php
PageInterface.php
PageSearchResultsInterface.php

The CMS module actually deals with two entities, one being Block and the other one being Page. Looking at the interfaces defined in the preceding code, we can see that we...