Free web hosting music - Transitive persistence synthetic identifiers, this solves the problem.
Transitive persistence synthetic identifiers, this solves the problem. New instances have a null identifier property value, so Hibernate treats them as transient. Detached instances have a nonnull identifier value, so Hibernate treats them accordingly. It s rarely necessary to customize the automatic detection routines built into Hibernate. The saveOrUpdate() method always knows what to do with the given object (or any reachable objects, if cascading of save-update is enabled for an association). However, if you use a natural composite key and there is no version or timestamp property on your entity, Hibernate has to hit the database with a SELECT to find out if a row with the same composite identifier already exists. In other words, we recommend that you almost always use saveOrUpdate() instead of the individual save() or update() methods, Hibernate is smart enough to do the right thing and it makes transitive all of this should be in persistent state, no matter if new or old much easier to handle. We ve now discussed the basic transitive persistence options in Hibernate, for saving new instances and reattaching detached instances with as few lines of code as possible. Most of the other cascading options are equally easy to understand: persist, lock, replicate, and evict do what you would expect they make a particular Session operation transitive. The merge cascading option has effectively the same consequences as save-update. It turns out that object deletion is a more difficult thing to grasp; the delete-orphan setting in particular causes confusion for new Hibernate users. This isn t because it s complex, but because many Java developers tend to forget that they re working with a network of pointers. Considering transitive deletion Imagine that you want to delete a Category object. You have to pass this object to the delete() method on a Session; it s now in removed state and will be gone from the database when the persistence context is flushed and committed. However, you ll get a foreign key constraint violation if any other Category holds a reference to the deleted row at that time (maybe because it was still referenced as the parent of others). It s your responsibility to delete all links to a Category before you delete the instance. This is the normal behavior of entities that support shared references. Any value-typed property (or component) value of an entity instance is deleted automatically when the owning entity instance is deleted. Value-typed collection elements (for example, the collection of Image objects for an Item) are deleted if you remove the references from the owning collection.
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