JPA entity design / cannot delete entity
- by timaschew
I though its simple what I want, but I cannot find any solution for my problem. I'm using playframework 1.2.3 and it's using Hibernate as JPA. So I think playframework has nothing to do with the problem.
I have some classes (I omit the nonrelevant fields)
public class User {
...
}
public class Task {
public DataContainer dataContainer;
}
public class DataContainer {
public Session session;
public User user;
}
public class Session {
...
}
So I have association from Task to DataContainer and from DataContainer to Sesssion and the DataContainer belongs to a User. The DataContainers can have always the same User, but the Session have to be different for each instance. And the DataContainer of a Task have also to be different in each instance. A DataContainer can have a Sesesion or not (it's optinal). I use only unidirectional assoc. It should be sufficient.
In other words: Every Task must has one DataContainer. Every DataContainer must has one/the same User and can have one Session.
To create a DB schema I use JPA annotations:
@Entity
public class User extends Model {
...
}
@Entity
public class Task extends Model {
@OneToOne(optional = false, cascade = CascadeType.ALL)
public DataContainer dataContainer;
}
@Entity
public class DataContainer extends Model {
@OneToOne(optional = true, cascade = CascadeType.ALL)
public Session session;
@ManyToOne(optional = false, cascade = CascadeType.ALL)
public User user;
}
@Entity
public class Session extends Model {
...
}
BTW: Model is a play class and provides the primary id as long type.
When I create some for each entity a object and 'connect them', I mean the associations, it works fine. But when I try to delete a Session, I get a constraint violation exception, because a DataContainer still refers to the Session I want to delete.
I want that the Session (field) of the DataContainer will be set to null respectively the foreign key (session_id) should be unset in the database. This will be okay, because its optional.
I don't know, I think I have multiple problems. Am I using the right annotation @OneToOne ?
I found on the internet some additional annotation and attributes:
@JoinColumn and a mappedBy attribute for the inverse relationship. But I don't have it, because its not bidirectional. Or is a bidirectional assoc. essentially?
Another try was to use @OnDelete(action = OnDeleteAction.CASCADE) the the contraint changed from NO ACTIONs when update or delete to:
ADD CONSTRAINT fk4745c17e6a46a56 FOREIGN KEY (session_id)
REFERENCES annotation_session (id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE CASCADE;
But in this case, when I delete a session, the DataContainer and User is deleted. That's wrong for me.
EDIT:
I'm using postgresql 9, the jdbc stuff is included in play, my only db config is
db=postgres://app:app@localhost:5432/app
