JPA Example Project

Follow the instructions point by point, run the code and check the results in the database. Check the states of in-memory objects as well (use the debugger, logging, or System.out).

Exercises

1. Create a PostgreSQL database jpaexampleDB and modify DB username and password in resources/META-INF/persistence.xml.
2. Start JPAExample. Student and Address are annotated with @Entity, so if you check the database you should see two tables created by Hibernate.
3. Use the @Column annotation to modify the default O-R mapping! Change the column name for attribute zipcode to Zip, limit its length to 4, and set the email field to UNIQUE and NOT NULL!
4. It is not needed to persist age of students since it is calculated from dateOfBirth - exclude it from the table by marking it @Transient.
5. Add a List<String> phoneNumbers to students, and add it to the constructor! You can fix the problem by @ElementCollection. Set the name of the auxiliary table to Phone.
6. Now students have an address. What happens when addresses have a student as well? Set a symmetric @OneToOne relation and see what happens!
7. We wouldn't want this... Fix the issue by adding a mappedBy attribute to the annotation! What has changed?
8. Annotate POJO Klass and convert it to an entity! The corresponding table should be called Class. Fix the issues (use @OneToMany)! What happened in the database?
9. Again, use mappedBy to make the association bidirectional! (You have to drop a table manually if it's not needed anymore.)
10. IMPORTANT! When using bidirectional relationships it is your responsibility to set the relations both ways to have the in-memory objects in sync with the database!
11. Create a new enumerated class called CCLocation with values MISKOLC, BUDAPEST, and KRAKOW! Add it as an attribute to Klass and set it in its constructor! How does it get represented in the database? Use the @Enumerated annotation to change this default behaviour!