Hibernate One-to-One Unidirectional mapping using join table

Question

I have the following table structure The Model Classes are :

Choice Class

@Entity
public class Choice {
@Id
  @GeneratedValue
  @Column(name="CHOICE_ID")
  private Long id;

  @Column(nullable=false)
  private String text;

}

Question Class

@Entity
public class Question {
   @Id
   @GeneratedValue
   @Column(name="QUESTION_ID")
   private Long id;

   private String text;

   @Column(name="CAT_ID")
   private Long catId = 1l;

   @Column(nullable=false)
   private int difficulty;

   @Column(nullable=false)
   private int set;

   @OneToMany
   @JoinColumn(name="QUESTION_ID", referencedColumnName="QUESTION_ID")
   private List<Choice> choices;

   @OneToOne
   @JoinTable(name = "RIGHT_CHOICE", joinColumns = { @JoinColumn(name = "QUESTION_ID",              referencedColumnName = "QUESTION_ID") })
   private Choice rightChoice;
}

Using annotations I would like to have both a One-to-Many relationship between question and choices. And a One to One relationship between Question and Right Choice. It would be better if both the relationships are unidirectional.

It would be helpful if someone could give a better table desgin.

Answer 1

I think that you do not need a RightChoice entity, because you can have a boolean inside your Choice entity.

@Table("CHOICE")
@Entity
class Choice {

<....>

@Column(name = "CORRECT")
private Boolean correct = false;

<....>


private Boolean getCorrect(){
   return correct;
}

}

And when you will construct a question, before add to question list, set one of choices as correct = true;

Choice choice = new Choice();
choice.setCorrect(true);
*<other choices are ommited intentionally>*
question.add(choice);
*<other adds are ommited intentionally>*

Also you should use OneToMany(cascade = CascadeType.PERSIST) inside your Question entity. This means that the persistence will propagate (cascade) EntityManager operation PERSIST to the relating entities.