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Econtainer null when loading EMF containment from Database using Hibernate

I have an EMF containment hierarchy: An House contains a list of Rooms, represented using an ecore file.
Before persisting, when I initially create my house and populate it with rooms, the eContainer value for a Room object correctly show the containing house. I then use Hibernate (no Teneo involved) to save the house (which cascade-saves the rooms).
When I reload the House object, I get references to all the Rooms. However, the eContainer value for a Room is now null. This is relevant because I use EcoreUtil.delete(bathroom) to delete a Room from its containing house, and that uses EObject.eContainer().
Relevant Hibernate Mapping:
<class name="House" table="house" lazy="false">
<bag name="rooms" lazy="true" cascade="save-update, delete">
<key update="true">
<column name="house_id" unique="false"/>
</key>
<one-to-many class="Room"/>
</bag>
</class>
<class name="Room" table="room" lazy="false">
</class>
What should I do to delete EMF objects? Should I call something other than EcoreUtil.delete(obj)? Should I manually add the eContainer references on load? Should I change my hibernate mapping?

Hibernate requires every property to have a getter and setter. In EMF (not using Teneo at least), there is a getter for Rooms but no setter.
public EList<Room> getRooms() {
if (rooms == null) {
rooms = new EObjectContainmentEList<Room>(Room.class, this, housePackage.HOUSE__ROOM);
}
return rooms;
}
I provided my own setter below.
public void setRooms(List<Room> roomList) {
this.rooms = new BasicEList<>();
this.rooms.addAll(roomList);
}
This was incorrect because a BasicEList does not do any provide EMF notification, so the eContainer was not getting set. I changed to the following, which in the underlying implementation uses a EObjectContainmentEList and so far it seems to work.
public void setRooms(List<Room> roomList) {
ECollections.setEList(getRooms(), roomList);
}

Does cascade="all-delete-orphan" inverse="true" work together?

This is my OrderSet.hbm file. It has OrderSetMembers as it's child (one-to-many) relationship.
<list name="orderSetMembers" lazy="true" cascade="all-delete-orphan" inverse="true">
<key column="order_set_id" not-null="true"/>
<list-index column="sequence_number"/>
<one-to-many class="OrderSetMember" />
</list>
This is my OrderSetMember.hbm file. OrderSetMember has a many-to-one relationship with its parent. I wanted a bi-directional mapping.
<many-to-one name="orderSet" class="OrderSet">
<column name="order_set_id"/>
</many-to-one>
Can the parent and the child both be saved with one session-save command?
Or do I need to have another session save to save the child as well?
Session session = sessionFactory.getCurrentSession();
session.saveOrUpdate(orderSet);
These are my data-models:
public class OrderSet {
private List<OrderSetMember> orderSetMembers;
}
public class OrderSetMember {
private OrderSet orderSet;
}

cascade and inverse have two completely different purposes.
cascade tells which entity lifecycle operation should be automatically applied on child(ren) when applied on parent.
inverse means that child is the owner of the association. That further means that if you don't associate child with the parent on the child side, the relationship information is not going to be synchronized with the database.
For example, if you add an OrderSetMember to the orderSetMembers collection in the parent entity instance, but you leave orderSet field null in the OrderSetMember instance, and then invoke session.saveOrUpdate(orderSet), the outcome will be:
Both OrderSet and OrderSetMember instances are saved to the database (save is cascaded to the children).
order_set_id (foreign key in the table to which OrderSetMember is mapped) is set to null. This is because OrderSetMember is the owner of the association, and there was no associated OrderSet entity when Hibernate inspected the owner of the association at dirty-check time.
When you read the above OrderSet instance in a new session, you'll notice that the OrderSetMember is not present in the orderSetMembers collection either.

Hibernate - setting null on the associated collection

I am trying to delete all the referenced entity in a collection of a parent entity by setting null on the collection.
For eg :
A is the parent class having one-to-many relation with class B.
Class A {
private Set<B> setB = new HashSet<B>();
}
The mapping is as follows :
<set name="setB " table="B" cascade="save-update" inverse="true">
<key column="FKey"></key>
<one-to-many class="B" />
</set>
a.setB(null);//a is persistent instance of A
The above call to set the collection as null is not deleting the entries in B. Has this anything to do with inverse = true.
Is it illegal to delete the child entities this way?

What about a.getB().clear();?

Inserting data using Hibernate Template

Consider the following:
User.java
class User{
...
private Set<Community> communities = new HashSet<Community>();
...
}
Community.java
class Community{
...
private Set<User> users = new HashSet<User>();
...
}
User.hbm.xml
<set name="communities" cascade="save-update" lazy="false" table="tbl_user_community">
<key column="user_id" />
<many-to-many class="Community" column="community_id"/>
</set>
Community.hbm.xml
<set name="users" lazy="false" cascade="save-update" table="tbl_user_community" inverse="true">
<key column="community_id" />
<many-to-many class="User" column="user_id"/>
</set>
both has many-to-many relationship.
Code for adding community to user:
HibernateTemplate template = null;
SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
template = new HibernateTemplate(sessionFactory);
User user = template.get(User.class, "100");
Community community = template.get(Community.class,1);
user.getCommunities().add(community);
template.saveOrUpdate(user);
Scenario:
community1 is assigned to user1 (inserted into database)
community2 is assigned to user1 (inserted into database)
community1 is assigned to user2 (inserted into database)
community2 is assigned to user2 (not inserted into database, throws NonUniqueObjectException)
if i use template.merge(user) instead of template.saveOrUpdate(user).. it works .. why???

saveOrUpdate() and update() take a detached object and attach this object instance to the session. So if an entity with the same type and ID is already attached to the session, Hibernate can't attach another instance: it would break the guarantee that only one entity with a given ID exists in a session. So it throws this exception.
merge() is different. It takes an detached entity, loads the entity with the same ID in the session if not already loaded, and copies the state (i.e. the fields) of the detached entity to the attached one. The detached entity stays deteached and unmodified.
So, in general, merge() should be preferred. BTW, the other methods don't exist in the JPA API. If you use saveOrUpdate(), you should generally call it as the first instruction of the transaction, to avoid being in the situation causing the NonUniqueException.

Beginners Hibernate problem - simple mapping with non-simple exception!

Please help me with this hibernate problem, I'm new to hibernate and still trying to get my head around it. I can't seem to work this issue out. I imagine I'm missing something pretty simple.
I've followed the example here to achieve a many-to-one mapping, as my requirements are almost identical: http://www.coderanch.com/t/217519/ORM/java/Hibernate-Newbie-Many-Relation-Tutorial
Please note that when I try to persist the Picture object, the user variable is (at that point in time) empty, as is every other variable bar image.
Also note that I've set hibernate to generate the database schema by itself via config in the hibernate config file.
Here are my mapping files (declarations removed)
User.hbm.xml
<class name="msc.model.User" table="USER">
<id name="id" column="USER_ID">
<generator class="native"/>
</id>
<property name="username"/>
<property name="email"/>
<bag name="pictures"
table="PICTURE"
lazy="true"
cascade="save-update">
<key column="PICTURE_ID"/>
<one-to-many class="msc.model.Picture" />
</bag>
</class>
And Picture.hbm.xml
<class name="msc.model.Picture" table="PICTURE">
<id name="id" column="PICTURE_ID">
<generator class="native"/>
</id>
<property name="story"/>
<property name="tattooist"/>
<property name="pic"/>
<many-to-one name="user"
class="msc.model.User"
column="USER" />
<property name="image" type="blob">
<column name="IMAGE" not-null="true" />
</property>
</class>
The class files (getters and setters stripped)
Picture.java
package msc.model;
import java.io.File;
import java.sql.Blob;
public class Picture {
private Long id = null;
private User user = null;
private File pic = null;
private String story = null;
private String tattooist = null;
private Blob image = null;
}
User.java
package msc.model;
import java.util.ArrayList;
import java.util.List;
public class User {
private Long id = null;
private String username = null;
private String email = null;
private List<Picture> pictures = null;
}
The persistence code (note that bFile is byte stream created from a file):
Session hib_ses = HibernateUtil.getSessionFactory().getCurrentSession();
hib_ses.beginTransaction();
Picture picture = new Picture();
picture.setImage(Hibernate.createBlob(bFile));
Long id = (Long) hib_ses.save(picture);
hib_ses.getTransaction().commit();
Here is the exception:
Cannot add or update a child row: a foreign key constraint fails (`msc`.`picture`, CONSTRAINT `FK85BE8DE2885129D` FOREIGN KEY (`PICTURE_ID`) REFERENCES `user` (`USER_ID`))
Please help!

There is something very strange going on if that is the real error you get.
Cannot add or update a child row: a foreign key constraint fails (`msc`.`picture`, CONSTRAINT `FK85BE8DE2885129D` FOREIGN KEY (`PICTURE_ID`) REFERENCES `user` (`USER_ID`))
This says that PICTURE.PICTURE_ID is a reference to USER.USER_ID. But PICTURE_ID is the PK of picture, which Hibernate will generate upon insertion. Did you mean to create a constraint from PICTURE.USER to USER.USER_ID?
Oh, I see you wrote you generate the schema via Hibernate. I think the error is in your "bag" definition. The key column should not be PICTURE_ID, but USER.

It looks like you are trying to save the Picture before saving the User. Try saving the User first.
[edit]
From the mapping - it looks like there is a Parent/Child relationship between User and Picture.
There is a good example in the Hibernate Documentation for a Parent Child relationship.
If you want the User to be able to be null, then a uni-directional relationship would be better.
[edit]
Another good reference about mapping collections with Hibernate.