JPA EmbeddedId is null after persisting - jpa

Question

Let's say I have 2 JPA entites
#Entity
public class MyComplexEntity implements Serializable {
private static final long serialVersionUID = 1L;
#EmbeddedId
#GeneratedValue(strategy = GenerationType.IDENTITY)
private MyComplexEntityId id;
private String text;
public MyComplexEntity() {
}
public MyComplexEntity(String text) {
this.text = text;
}
public MyComplexEntityId getId() {
return id;
}
public void setId(MyComplexEntityId id) {
this.id = id;
}
public String getText() {
return text;
}
public void setText(String text) {
this.text = text;
}
#Override
public String toString() {
return "MyComplexEntity{" + "id=" + id + ", text=" + text + '}';
}
}
and
#Embeddable
public class MyComplexEntityId {
#Column
private long id;
public MyComplexEntityId(long id) {
this.id = id;
}
public MyComplexEntityId() {
}
public long getId() {
return id;
}
public void setId(long id) {
this.id = id;
}
#Override
public String toString() {
return "MyComplexEntityId{" + "id=" + id + '}';
}
}
Now I'm trying to persist a new MyComplexEntity object like this
MyComplexEntity entity = new MyComplexEntity("something");
em.persist(entity);
System.out.println(entity);
and what I get is this:
MyComplexEntity{id=null, text=something}
Why is the id null there? If I do the same thing with a primitive primary key type, the id is correctly set after persisting. I've also tried the following things:
Calling em.flush(); after the persist: does nothing
Calling em.refresh(entity); after the persist: Exception telling me that the entity is no longer in the database (which is wrong)
Trying em.merge() instead of em.persist(): Same result, as expected
Calling em.contains(entity); returns true, so the entity is actually attached
Putting the em.persist(); in a separate transaction by executing it in a separate method using #TransactionAttribute(TransactionAttributeType.REQUIRES_NEW)
There has to be some kind of problem with persist(); when using an #EmbeddedId, but I just don't get it.

Answer 1

You cannot put GeneratedValue(strategy = GenerationType.IDENTITY) on a complex mapping. It needs to go within the embeddedId class, and you need to instantiate a MyComplexEntityId instance for your new Entity. You will also need to flush to the database to ensure that values are assigned as identity values are assigned by the insert.