@Embeddable
class Y {
protected Y(){}
@Column(nullable = false)
int i;
@Column(nullable = false)
int j;
}
@Entity
class X {
protected X(){}
@Id
@Column(name = "id")
int id;
@ElementCollection(fetch = FetchType.EAGER)
Set<Y> s = new HashSet<>();
}
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
X a = new X();
a.s.add(new Y());
session.save(a);
transaction.commit();
session.close();
Hibernate map the table x_s contain 3 column which is id of x, i and j. However, if make a detached object to persisted again by update like:
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
X x = session.get(X.class, 0);
transaction.commit();
session.close();
Session session1 = sessionFactory.openSession();
Transaction transaction1 = session1.beginTransaction();
session1.saveOrUpdate(x); // and select or update should execute
transaction1.commit();
session1.close();
The strange thing is, except the select, hibernate will do delete and insert, the above code will generate:
Hibernate: select x0_.id as id1_0_0_, s1_.X_id as X_id1_1_1_, s1_.s_i as s_i2_1_1_, s1_.s_j as s_j3_1_1_ from X x0_ left outer join X_s s1_ on x0_.id=s1_.X_id where x0_.id=?
Hibernate: delete from X_s where X_id=? and s_i=? and s_j=?
Hibernate: insert into X_s (X_id, s_i, s_j) values (?, ?, ?)
Hibernate: select x_.id from X x_ where x_.id=?
Hibernate: delete from X_s where X_id=? and s_i=? and s_j=?
Hibernate: insert into X_s (X_id, s_i, s_j) values (?, ?, ?)
According to this answer, it says the reason is table x_s has no pk. But the table x_s generated by hibernate use all 3 column as a combined pk already.
It seems the only way to eliminate those insert and delete commands is change Set<Y> to List<Y>, hibernate will automatically add a column order and combine order and x_id as pk. But from db schema view, it is no material difference
P.S I use hibernate 5.3
