In this chapter we have reverse engineered the 3T database into a set of Java classes. Each Java class represents a JPA entity with annotations defining the relationship between entities as well as the mapping of database columns to Java fields. We have had a brief introduction to JPQL through named query definitions and introduced key JPA annotations.

Although this chapter has introduced many key concepts, the scope of JPA and JPQL leaves much for you to learn. JPA is a key tool in enterprise application development, allowing for easy enhancements and database-agnostic programming.

The next chapter will introduce the Data Access Object (DAO) design pattern and implement a robust data access layer using the domain classes we have just defined. Our JPA journey has just started!