Hibernate: How to fix “identifier of an instance altered from X to Y”?

Question

org.hibernate.HibernateException: identifier of an instance 
of org.cometd.hibernate.User altered from 12 to 3

in fact, my user table

Answer 1

Make sure you aren't trying to use the same User object more than once while changing the ID. In other words, if you were doing something in a batch type operation:

User user = new User();  // Using the same one over and over, won't work
List<Customer> customers = fetchCustomersFromSomeService();
for(Customer customer : customers) {
 // User user = new User(); <-- This would work, you get a new one each time
 user.setId(customer.getId());
 user.setName(customer.getName());
 saveUserToDB(user);
}

Answer 2

In my case getters and setter names were different from Variable name.

private Long stockId;
    public Long getStockID() {
        return stockId;
    }
    public void setStockID(Long stockID) {
        this.stockId = stockID;
    }

where it should be

public Long getStockId() {
    return stockId;
}
public void setStockId(Long stockID) {
    this.stockId = stockID;
}

Answer 3

Are you changing the primary key value of a User object somewhere? You shouldn't do that. Check that your mapping for the primary key is correct.

What does your mapping XML file or mapping annotations look like?

Answer 4

I was facing this issue, too.

The target table is a relation table, wiring two IDs from different tables. I have a UNIQUE constraint on the value combination, replacing the PK. When updating one of the values of a tuple, this error occured.

This is how the table looks like (MySQL):

CREATE TABLE my_relation_table (
  mrt_left_id BIGINT NOT NULL,
  mrt_right_id BIGINT NOT NULL,
  UNIQUE KEY uix_my_relation_table (mrt_left_id, mrt_right_id),
  FOREIGN KEY (mrt_left_id)
    REFERENCES left_table(lef_id),
  FOREIGN KEY (mrt_right_id)
    REFERENCES right_table(rig_id)
);

The Entity class for the RelationWithUnique entity looks basically like this:

@Entity
@IdClass(RelationWithUnique.class)
@Table(name = "my_relation_table")
public class RelationWithUnique implements Serializable {

  ...

  @Id
  @ManyToOne
  @JoinColumn(name = "mrt_left_id", referencedColumnName = "left_table.lef_id")
  private LeftTableEntity leftId;

  @Id
  @ManyToOne
  @JoinColumn(name = "mrt_right_id", referencedColumnName = "right_table.rig_id")
  private RightTableEntity rightId;

  ...

I fixed it by

// usually, we need to detach the object as we are updating the PK
// (rightId being part of the UNIQUE constraint) => PK
// but this would produce a duplicate entry, 
// therefore, we simply delete the old tuple and add the new one
final RelationWithUnique newRelation = new RelationWithUnique();
newRelation.setLeftId(oldRelation.getLeftId());
newRelation.setRightId(rightId);  // here, the value is updated actually
entityManager.remove(oldRelation);
entityManager.persist(newRelation);

Thanks a lot for the hint of the PK, I just missed it.

Answer 5

In my case it was because the property was long on object but int in the mapping xml, this exception should be clearer

Answer 6

You must detach your entity from session before modifying its ID fields