Hibernate: 3.3.1.GA
Annotation 3.4.0.GA
EntityManager 3.4.0.GA

Hi,

I read some parts of the book titled "Java Persistence with Hibernate". It says:


and he uses this code:



But when I try the same thing (deleting a detached object) it gives me this exception:



Now I'm really confused.

My code in deleting an object:



I just want to confirm if what's written in the book is correct or not, if the detached object could be deleted without re-attaching it to a persistent context. And if it does requires re-attachment, what's the best way to do it, it's just doesn't look good if it's going to issue an insert statement before issuing a delete statement as what happens if you call merge() method.

For now, my solution is to load a persistent object by copying the id of detached object and use the persistent object to delete what my detached object is representing.

Thanks.

Hi unrealdummy,

What you read in the book, is correct -


This is correct if you use Hibernate Native for Peristence.
As you know Hibernate also implement (partially) JPA specification throw using (that what you are using ), then it follow the JPA specification. If you go future in Same Chapter Of book ("JAVA Persistence with Hibernate") then it clearly tell you can't delete Detach object Directly through JPA implementor . you have to attach it with with Persistence Context.

And for the problem, as you mention



you can use this alternative approach -
- Load the object in persistence context without hitting the database. Use API of EntityManager.
- Now you can call API to remove it.

Hi parmendratyagi

Thanks for a quick response.

After reading that part of the book twice, I figured out what I was doing wrong.

I believe I am seriously misled by the exception's description:



There's nothing wrong with deleting detach objects, what I was really doing before when that exception was thrown was, I was deleting a transient object, but the exception clearly states that I was trying to delete a "detached" object instead of saying I was trying to delete a "transient" object.

I tried deleting a detach objects and it was good. The difference between a transient and detached object wasn't clear to me until I read the book twice and tried experimenting with it.

So, I believe it's not really about whether I'm using a "JPA version" of hibernate or native hibernate.



Though your response made me make experiment using native Hibernate and it turns out that it is OK to delete a transient object, so you made half of the point valid. There's a difference between JPA hibernate and native with regards to handling transient objects, but not with regards to detached objects.

I'm sorry I was just a bit confused, and really, the exception is very misleading, it must have said:

"Removing a transient instance com.samples.MyEntity#30"

instead of:

"Removing a detached instance com.samples.MyEntity#30"

when I was really using a transient instead of detached object.

So there's no way of directly deleting an object without that object going from a persistent state after all, ei? Because in the graph shown in the book, there's no transition from transient to detached state without taking a path to persistent state. The graph was even incomplete, it doesn't show a path from detached state to removed state.

I think we're done here, thanks anyways, please post a reply if you think I'm missing something or you want to add up something that could help me understand more about this matter.

Hi unrealdummy,

Thanks for the sharing the information.

I thing, you were assigning value to the identifier property of transient object before calling delete on that object, only so Hibernate was detecting it as detached object.