Issue in Mapping for Hibernate JPA

Question

I have a datamodel, which has:

• a User entity which has a few fields specific to 2 users in the application
• another entity UserDetails , which contains details specific to one particular type of user in the application besides the fields in User entity

Both entities share the same primary key. I am new to JPA. What kind of mappings should be there between the two?

@Entity
class User{
  @Id
  @Column(name="USER_ID")
  private int id;
}


@Entity
class UserDetails{
  @Id
  @OneToOne(optional = false, fetch = FetchType.EAGER)
  @JoinColumn(name = "USER_ID")
  private User user;

  ...
}

The above mapping gives issues on fetching UserDetails for a particular User .

It requires that both Entities share the same primary key USER_ID.

Answer 1

You didn't mention the issues with the above mapping. It looks OK, but I would use a separate primary key for UserDetails table.

@Entity
class UserDetails{
  @Id
  private int id;

  @OneToOne(optional = false, fetch = FetchType.EAGER)
  @JoinColumn(name = "USER_ID")
  private User user;

  ...
}

Also, it is a good practise to use bidirectional relationships , for eaiser navigation ie getting user details from User , you would just use user.getUserDetails(); so in User class:

@Entity
class User{
  @Id
  @Column(name="USER_ID")
  private int id;

  @OneToOne(mappedBy = "user")
  private UserDetails userDetails;
}

Answer 2

In this case use OneToOne relationship. But make sure your database table UserDetails has foreign key relationship to User table. Use below code to implement it using JPA and Hibernate .

@Entity
class User{
  @Id
  @Column(name="USER_ID")
  private int id;

  // getters and setters
}


@Entity
class UserDetails{
  @Id
  @Column(name="USER_DETAILS_ID")
  private int userDetailsId;

  @OneToOne(optional = false, fetch = FetchType.LAZY)
  @JoinColumn(name = "USER_ID")
  private User user;

  // getters and setters
}