Hi

My goal is to cleanly detach an object when it has MayToMany to another object and it is not requested by user.

I have a ManyToMany relation between two objects

Role
{
@ManyToMany(fetch=FetchType.LAZY)
@JoinTable(...)
public Collection<User> getUsers()
{
return users;
}
}

Class User
{
// manytomay to Roles
}

1. i restart my server to make sure that there are no pending flushes.
2. my goal is to get a list of Roles (without the list of users per role)

When i just want to get a list of roles , i want cleanly detach Role POJO so that getUsers() should give me a new ArrayList or null.

however, when i initialize the users to new ArrayList(), i notice that hibernate

is processing ACTION_PERSIST_ON_FLUSH on the users and there fore, then executes

delete from Role_User where role.id =?

and deletes all my users associated with role. from Role_User table

I do not see this happen to ManyToOne relation.

Questions:

1. what do i set the collection of users to so that i do not see data being deleted from database?
2. if there is any other solution to achieve the same.

Help is very much appreciated as i have broken my head on this for a long time.

thanks
Sudhir

If you set the users collection of role to a new (empty) array list while the session is open then hibernate will interpret that as deleting all the users from that role.

Your requirements sound a little odd. Calling getUsers should return the users if there are some. Returning an empty list instead just strikes me as wrong. Either you shouldn't be calling that method in your scenario or it should be pre-initialised with the users form the role.

thanks for the reply



I have two modes in which an object is populated
- notDeep ==> where only its attributes and relations marked eager are populated
- deep ==> where its attributes and all relations are populated.

My requirement is to serialize POJOs to XML outside the session in the client code. So, i iterate thru all attributes and relations to build the XML. If i find a relation populated, i serialize the relation to XML as well.
Now, i get this lazyInitError if i access a PersistentBag outside session, which is valid. I am looking for a solution to avoid that exception and have the POJO not have any Persistence pointers/references

in non-deep mode
<role name="rr">
</role>

in deep mode
<role name="rr">
<user name="ss"/>
<user name="dd"/>
</role>

i did download a HibernateCleaner piece of code, but when i run that it removes all peristence references but it always populates ManyToMany relations.

i hope my requirement was clear enough. Your thoughts will be appreciated.

So you make a request to get an object in either "deep" or "shallow" mode therefor you already know what kind of data you're going to get back. The XML generator should take account of the data request you made. e.g.

yes i could do that. however that does not cover the scenario when the same pojo is being passed around between session beans for processing. for example, if i there is a bean to add on other information to the role object being passed, will hibernate not throw an exception if i want to add another user to the user collection?

is there a way to know if the PersistentBag has been executed to populate itself.

i know executing size() on the bag executes the query, if it is already not done. is there a flag that indicates whether the query is done or not?

If you're passing the role between session beans in the same transaction then the hibernate session that loaded the object initially should still be open (unless you're explicitly closing it) so fetching users should be fine.

I'm not sure there's a way of checking whether collections are initialised before accessing them but needing to do so just sounds wrong to me.

whats wrong is when hibernate persists/merges onetoMany or manyToOne only when persist/merge methods are called, why does it handle differently for ManyToMany.

if you are given a POJO and there are public methods there should be no restrictions of not calling it. If EJB3 says that detatching the object from entutymanager creates the value object to be passed around, it should be cleaned up correctly.

anyways, workarounds need to be written i guess.

thanks for your time and help.