一对一休眠-未分配ID

Question

On my unit tests I get the JpaSystemException: ids for this class must be manually assigned before calling save() error . I have reworded my entities to make the question shorter and more readable.

So student has an optional one to one relation with the table EnrolledInfo.

Student Entity

@Entity
@Table(name = "Student")
public class Student  {

    @Id
    @Column(name = "studentId")
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long studentId;

    @OneToOne(fetch = FetchType.LAZY, mappedBy = "student", cascade = CascadeType.ALL)
    private EnrolledInfo enrolledInfo;

    private String firstName;

    private String lastName;

    // setters&getters etc..    
}

EnrolledInfo Entity

@Entity
@Table(name = "EnrolledInfo")
public class EnrolledInfo implements Serializable {

    @Id
    private Long studentId;

    @OneToOne(fetch = FetchType.Eager)
    @PrimaryKeyJoinColumn
    @JsonBackReference
    private Student student;

    @Column(name = "enrolledDate")
    private Date enrolledDate;

    @Column(name = "paidTuition")
    private Boolean paidTuition;

    // setters&getters etc..
}

Putting it together in a test (this errors)

Surely I dont have to save the enrolledInfo entity before I save the student one?

@Test
public void student_test() {

  Student student = new Student();
  EnrolledInfo enrolledInfo = new EnrolledInfo(); 
  enrolledInfo.setPaidTuition(true);

  student.setEnrolledInfo(enrolledInfo);        
  studentDao.save(student);
  // errors on // JpaSystemException: ids for this class must be manually assigned before calling save():
}

Answer 1

Your EnrolledInfo has studentId as its Id, and no generation strategy cause its ids comes from the relationship as it is its parent id (the student). For that to work the student must be known during the save.

So the EnrolledInfo must know its student, jpa does not handle both sides of relationship itself, so they can be set manually.

  Student student = new Student();
  EnrolledInfo enrolledInfo = new EnrolledInfo(); 
  enrolledInfo.setPaidTuition(true);
  enrolledInfo.setStudent(student);

  student.setEnrolledInfo(enrolledInfo);        
  studentDao.save(student);

Now in JPA2, the proper annotation would be:

@Entity
@Table(name = "EnrolledInfo")
public class EnrolledInfo implements Serializable {

    @Id
    private Long studentId;

    @OneToOne(fetch = FetchType.Eager)
    @Id
    @JsonBackReference
    private Student student;

in JPA1 with @PrimaryKeyJoinColumn you would need to provide the full mappings (you should now use the JPA2, so there is no reason for the old one but just in case):

@Entity
@Table(name = "EnrolledInfo")
public class EnrolledInfo implements Serializable {

    @Id
    @Column(name="STUDENT_ID")
    private Long studentId;

    @OneToOne(fetch = FetchType.Eager)
    @PrimaryKeyJoinColumn(name="STUDENT_ID", referencedColumnName="STUDENT_ID")
    @JsonBackReference
    private Student student;