Hibernate Won't Update My Object!

Yesterday, I was given a Hibernate related bug to fix. We have an object, say object A which has a list of object B. This list of object B are stored as a JSON string in table A.

So here’s the problem, after calling a session.update on object A with the updated object B, the change was not persisted into the database. After hours of Googling and some help from Michael who is a fellow colleague of mine, I found the problem.

According to this article, Hibernate will only do a UPDATE statement after session.flush(). During this operation, Hibernate will compare the original object and the object to be updated.

This article explains how Hibernate compares the object.

The fix? In your Hibernate user type, override the deepCopy and return another instance of list.

@Override
public Object deepCopy(Object value) throws HibernateException
{

  // if value is null, return null
  if(value == null)
  {
    return null;
  }

  // convert the value to a List first
  List<ObjectB> objectBList = (List<ObjectB>)value;

  // create a new Arraylist and add all the objects
  List<ObjectB> newObjectBList = new ArrayList<ObjectB>();
  for(ObjectB objectB : objectBList)
  {
    newObjectBList.add(objectB);
  }
  return newObjectBList;
}