I had the same problem, and this is what I found: The merge method traverses the graph of the object that you want to store, and for each object in this graph it loads it from the database, so it has a pair of (persistent entity, detached entity) for each object in the graph, where … Read more
Suppose you have an Order and an OrderLine. You can choose to have a unidirectional OneToMany between Order and OrderLine (Order would have a collection of OrderLines). Or you can choose to have a ManyToOne association between OrderLine and Order (OrderLine would have a reference to its Order). Or you can choose to have both, … Read more
I am not really sure about your question (the meaning of “empty table” etc, or how mappedBy and JoinColumn were not working). I think you were trying to do a bi-directional relationships. First, you need to decide which side “owns” the relationship. Hibernate is going to setup the relationship base on that side. For example, … Read more
If you are using hibernate as your JPA provider you can use the annotation @OnDelete. This annotation will add to the relation the trigger ON DELETE CASCADE, which delegates the deletion of the children to the database. Example: public class Parent { @Id private long id; } public class Child { @Id private long id; … Read more
The meaning of CascadeType.ALL is that the persistence will propagate (cascade) all EntityManager operations (PERSIST, REMOVE, REFRESH, MERGE, DETACH) to the relating entities. It seems in your case to be a bad idea, as removing an Address would lead to removing the related User. As a user can have multiple addresses, the other addresses would … Read more