Bi-Directional ManyToOne

In a bi-directional, many-to-one relationship, the owning side is mapped just like its uni-directional counterpart.

@Entity
public class Film {
  // ...
  @ManyToOne
  @JoinColumn(name="language_id")
  private Language language;
  // ...
}

In the non-owning entity of a bi-directional relationship, add the @OneToMany annotation above the field that references the owning entity.

• Use the mappedBy element on the @OneToMany annotation to specify the defining field in the owning entity.

@Entity
public class Language {
  // ...
  @OneToMany(mappedBy="language")
  private List<Film> films;
  // ...
}

• Make the field of type Collection, List, or Set and give it a plural name.

Drill

1. Create a bi-directional, many-to-one relationship between your Film and Language entities.

2. Modify Film, add a field of type Language annotated with @ManyToOne and @JoinColumn.

3. As a bi-directional relationship, the Language entity must also be updated. Add a field of type List<Film>, annotate it with @OneToMany, and set the mappedBy element to the corresponding field in Film.

4. Also, add get and set methods in each class for the new fields.

5. Update your JUnit tests for Film and Language to verify that the association works successfully in both directions.


---

Prev -- Up -- Next