JPA - Entity design problem

Question

I am developing a Java Desktop Application and using JPA for persistence. I have a problem mentioned below:

I have two entities:

• Country
• City<

Answer 1

IMO the proper way to deal with such issues would be to use a generated internal (typically Long) ID instead of a natural primary key - this eliminates the whole problem. Of course, this requires a modification of your DB schema, but from your post I assume that this is possible.

@Entity
public class City implements Serializable {
    private Long id;

    private String name;
    private Country country;

    @Id
    @GeneratedValue
    @Column(name = "CITY_ID")
    public Long getId() {
        return this.id;
    }
    private void setId(Long id) {
        this.id = id;
    }

    // more getters, setters and annotations
}

Answer 2

countryName in CityPK should be marked read-only using @Column(insertable = false, updatable = false) and both countryNames should be mapped to the same column (using name property):

  @Entity
  public class City implements Serializable {
           @EmbeddedId
           private CityPK cityPK;

           @ManyToOne
           @JoinColumn(name = "countryName")
           private Country country;
  }


   @Embeddable
   public class CityPK implements Serializable {
       public String cityName;

       @Column(name = "countryName", insertable = false, updatable = false)
       public String countryName;
   }