Hibernate JPA IdentifierGenerationException: null id generated for class with @embeddedid

Question

I am having trouble mapping my database domain model to the program entities in one case where the entity is essentially a join table (a period) which combines two other entities (a timeslot and a day). Another entity (a lesson) then has a reference to this period entity, determining when it occurs.

When I try to save a lesson with a new period using saveOrUpdate(lesson) hibernate throws an IdentifierGenerationException

org.hibernate.id.IdentifierGenerationException: null id generated for:class com.trials.domain.Period

The database looks like below (not the real database, just the key tables and columns)

In the java hibernate model, I have used an embedded id for the primary key of the period class and the lesson class then has a reference to a period.

Period.java

@Entity
@Table(name = "period")
public class Period{
    @EmbeddedId
    private PeriodId periodId;

    @ManyToOne(fetch = FetchType.EAGER)
    @JoinColumn(name = "day_idday", nullable = false, insertable = false, updatable = false)
    private Day day;

    @ManyToOne(fetch = FetchType.EAGER)
    @JoinColumn(name = "timeslot_idtimeslot", nullable = false, insertable = false, updatable = false)
    private Timeslot timeslot;

    //constructors, getters, setters, hashcode, and equals
}

And the embedded id just has the primary key columns:

PeriodId.java

@Embeddable
public class PeriodId implements Serializable {
    @Column(name = "timeslot_idtimeslot")
    private int timeslotId;

    @Column(name = "day_idday")
    private int dayId;

    //constructors, getters, setters, hashcode, and equals
}

Then there is the lesson class that uses the period defined as:

Lesson.java

@Entity
@Table(name = "lesson")
public class Lesson {
    @Id
    @Column(name = "idlesson")
    private int lessonId;

    @ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
    @JoinColumns({@JoinColumn(name = "period_timeslot_idtimeslot", nullable = false, updatable = false), @JoinColumn(name = "period_day_idday", nullable = false, updatable = false)})
    private Period period;
    //constructors, getters, setters, hashcode, and equals
}

The Timeslot and Day entity classes are both very basic pojos, and their ids use GenerationType.AUTO. So my problems are:

1. What causes this IdentifierGenerationException
2. How to avoid it while keeping the same database model

Thanks in advance

Answer 1

Put those guys

@ManyToOne(fetch = FetchType.EAGER)
@JoinColumn(name = "day_idday", nullable = false, insertable = false, updatable = false)
private Day day;

@ManyToOne(fetch = FetchType.EAGER)
@JoinColumn(name = "timeslot_idtimeslot", nullable = false, insertable = false, updatable = false)
private Timeslot timeslot;

inside the PeriodId class and throw away those ints. I have done a mapping similar to yours this way and it works.