Hibernate version: 2.1.3 & 2.1.6
Please help me about this confusing cascade of Hibernate:
I thought in any case when I set the cascade=none(on parent or one side in an association), the delete action of parent must cause an exception to be thrown, because when I set cascade=none, Hibernate supposed to don't react in a save-update or delete manner, but here it reacts in save-update manner.
I want to have a bidirectional one-2-many association, and when I want to delete the parent (which has at least one child), the hibernate throws an exception about foreign key constraint violation. I don't want hibernate delete the parent side and update all the children's foreign key to null (what I got as the result). So what should I do?

Lots of posts and information on this one. You need to mark the collection as inverse="true" which tells Hibernate that you will manage the relationship from the child side of things, otherwise Hibernate thinks the relationship is managed from the parent side. So, what happens is when you delete the parent Hibernate removes the relationship first by updating the child object to set its relationship field to null. Here's the sequence so you can understand it (Hibernate gurus, please correct me if I'm wrong...)

Inverse="false", cascade="none"
1. User deletes parent
2. Hibernate senses the relationships are being deleted
3. Hibernate updates child objects' relationship field to NULL, effectively deleting the relationship (this may result in a Foreign Key violation, if the column is not nullable in the DB)
4. Hibernate deletes the parent, orphaning the children

Inverse="true", cascade="none"
1. User attempts to delete parent
2. Hibernate senses the relationships are attempting to be deleted
3. Hibernate throws an exception

Please experiment with that and see what happens. Also, read and re-read the documentation and web site articles on inverse="true" relationships. Understanding that is crucial to understanding how hibernate works with relationships.