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Hibernate version:
3.x
Mapping documents:

Code between sessionFactory.openSession() and session.close():
merge(obj)

Name and version of the database you are using:
MySQL

I have a class with more than one collection data type children something like the followings:

Since this class is quite big, we don't fetch all its children set for one usage. When we only consider one set of its children, we only fetch an instance of this class and the set of children. If we need to update one set of children, bSet for example, only. How it can be done with in Hibernate? Shall we fetch all of its children sets so that the Hiberneate knows which children set is dirty and update it. Or I have to use native SQL to handle it?