In this chapter, we used JPA to create our Spring Boot application database. First, we created entity classes, which are mapped to database tables. Then, we created CrudRepository for our entity class and that provides CRUD operations for the entity. After that, we managed to add some demo data to our database by using CommandLineRunner. We also created one-to-many relations between two entities. At the beginning of the chapter, we used the H2 in-memory database, while at the end, we switched the database to MariaDB. In the next chapter we will create RESTful web service to our backend.