Hibernate does not delete a DB record when an entity is removed from a collection

Question

Simply removing an entity from a collection of related entities, will not delete the database record, right?

for example:

currentUser.getBooks().remove(thisBook);
userDAO.update(currentUser);

won't delete the record from the DB

Do I have to always explicitly go to the bookDAO and say session.delete(thisBook) every time? I though that Hibernate is much smarter than that and does cascading checks when a parent entity is saved or updated.

How do I resolve this?

Answer 1

Removing entity Book from the books collection in entity User just removes the relationship between the two entities ( Book and User ), not the Book entity instance.

The CASCADE clause is also not what you are looking for. Cascading means that if User has books , that is a collection of Book instances, when you remove a User instance, then the book instances are removed as well.

So, read getBooks().remove(thisBook) as remove this book from this collection and not from the database .

And yes, if you want to remove the book you have to use session.remove(book) (or the facility in you DAO).

Answer 2

You need to specify the cascade type on your relationship.

examples here: http://www.mkyong.com/hibernate/hibernate-cascade-example-save-update-delete-and-delete-orphan/

Answer 3

这完全取决于您在图书收藏集中定义的层叠属性。