Detach an entity from JPA/EJB3 persistence context

Question

What would be the easiest way to detach a specific JPA Entity Bean that was acquired through an EntityManager. Alternatively, could I have a query return detached objects in

Answer 1

As far as I know, the only direct ways to do it are:

1. Commit the txn - Probably not a reasonable option
2. Clear the Persistence Context - EntityManager.clear() - This is brutal, but would clear it out
3. Copy the object - Most of the time your JPA objects are serializable, so this should be easy (if not particularly efficient).

Answer 2

Do deal with a similar case I have created a DTO object that extends the persistent entity object as follows:

class MyEntity
{
   public static class MyEntityDO extends MyEntity {}

}

Finally, an scalar query will retrieve the desired non managed attributes:

(Hibernate) select p.id, p.name from MyEntity P
(JPA)       select new MyEntity(p.id, p.name) from myEntity P

Answer 3

I think you can also use method EntityManager.refresh(Object o) if primary key of the entity has not been changed. This method will restore original state of the entity.

Answer 4

Since I am using SEAM and JPA 1.0 and my system has a fuctinality that needs to log all fields changes, i have created an value object or data transfer object if same fields of the entity that needs to be logged. The constructor of the new pojo is:

    public DocumentoAntigoDTO(Documento documentoAtual) {
    Method[] metodosDocumento = Documento.class.getMethods();
    for(Method metodo:metodosDocumento){
        if(metodo.getName().contains("get")){
            try {
                Object resultadoInvoke = metodo.invoke(documentoAtual,null);
                Method[] metodosDocumentoAntigo = DocumentoAntigoDTO.class.getMethods();
                for(Method metodoAntigo : metodosDocumentoAntigo){
                    String metodSetName = "set" + metodo.getName().substring(3);
                    if(metodoAntigo.getName().equals(metodSetName)){
                        metodoAntigo.invoke(this, resultadoInvoke);
                    }
                }
            } catch (IllegalArgumentException e) {
                e.printStackTrace();
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            } catch (InvocationTargetException e) {
                e.printStackTrace();
            }
        }
    }
}

Answer 5

If there aren't too many properties in the bean, you might just create a new instance and set all of its properties manually from the persisted bean.

This could be implemented as a copy constructor, for example:

public Thing(Thing oldBean) {
  this.setPropertyOne(oldBean.getPropertyOne());
  // and so on
}

Then:

Thing newBean = new Thing(oldBean);

Answer 6

If you get here because you actually want to pass an entity across a remote boundary then you just put some code in to fool the hibernazi.

for(RssItem i : result.getChannel().getItem()){
}

Cloneable wont work because it actually copies the PersistantBag across.

And forget about using serializable and bytearray streams and piped streams. creating threads to avoid deadlocks kills the entire concept.