Multiple representations of the same entity are being merged, Detached - jpa

Question

I have been getting an error while trying to update a list of entities containing persisted entity and detached entity both (newly created entity) into my db using jpa2.0.
My entity contains internal entities which are giving an error (mentioned in the title) when merging the data:
Class superclass{
private A a;
private string name;
//getter setters here...
}
Class A{
private long id;
#onetoone(cascade=CascadeType.All, fetch=FetchType.Eager)
private B b;
#onetoone(cascade=CascadeType.All, fetch=FetchType.Eager)
private C c;
//getter setters here...
}
Class Dao{
daoInsert(superclass x){
em.merge(x);
}
}
I want any entity sent for persisting to be merged into the db.
Hibernate does provide solution for this by adding the following to the persistence.xml
Is there something I can do in jpa same as hibernate.
Please do not suggest to find the entity using em.find() and then update manually because I need both entities the persisted entity and the newly created entity too.
Also I'm using spring form to persist the entire patent entity into db.
I am sorry if I'm not clear enough, this is my first question and I'm really a beginner.
Any help will be most appreciated.

Answer 1

Found an answer to the question myself today.You just need to
remove CascadeType.MERGE from the entity that is not allowing you to persist the detached entity.
if you're using CascadeType.ALL then mention all cascade type other than CascadeType.MERGE.

Answer 2

Now removing CascadeType.MERGE from cascade is one solution but not a best solution because after removing MERGE from Cascade you won't be able to update the mapped object ever.
If you want to merge the Detached entity with Hibernate then clear the entity manager before you merge the entity
entityManager.clear();
//perform modification on object
entityManager.merge(object);

Answer 3

To solve this problem make sure to specify that the identifiers of your objects are automatically generated by adding #GeneratedValue(strategy = GenerationType.IDENTITY) on the identifaint such as id.
In this way when the merge will be carried out, the identifier of the elements to merge will be automatically incremented, compared to the other object already recorded in the database to avoid primary key conflicts