In this chapter, we have seen how we can use Spring Data to add a persistence layer to the core microservices. We used the core concepts of Spring Data, repositories and entities, to store data in both MongoDB and MySQL using a programming model that is similar, even though not fully portable. We have also seen how Spring Boot's annotations, @DataMongoTest and @DataJpaTest, can be used to conveniently set up tests targeted for persistence; this is where an embedded database is started automatically before the test runs, but no other infrastructure that the microservice will need in runtime, for example, a web server such as Netty, is started up. This results in persistence tests that are easy to set up and that start with minimum overhead.
We have also seen how the persistence layer can be used by the service layer and how we can add APIs for creating and...