Werner, Since you have data associated with your many-to-many, you can simplify this by making an entity in the middle, transforming your many-to-many in to a many-to-one, one-to-many from the ORMs perspective.
We can continue this discussion on the Hibernate forum, if you like. I'd be glad to help you out. [EMAIL PROTECTED] > -----Original Message----- > From: news [mailto:[EMAIL PROTECTED] On Behalf Of Werner Punz > Sent: Thursday, September 15, 2005 2:54 AM > To: [email protected] > Subject: Re: Hibernate: 1-to-many --> struggling > > Well maybe the original guy did not use session.saveOrUpdate > on the parent element... > > I usually deal with 1:n which usually are far less > problematic then m:n (which is the case where you usually > sink 90% of the dev time banging your head and cursing > hibernate left and right) is to have a 1:n rel, with a set > mapping and to use cascade all with a save on the root element. > That has worked best. > > The crux of hibernate is, you have so many ways to solve > things for everything around 100 ways, but 90 of them fail > with either no error or cryptic error messages once you have > to apply them, while there still is a huge lack of best > practices especially in the areas many-to-many and one-to-many > > I will give an example: > Implicit mapping, not working if you have additional data in > your many to many binding table, now how do you resolve that > you can resolve it via an explicit binding object > declaration, the doc is very vague on this approach, > > you finally get it up and running, loading works, but > deleting utterly fails with a cascade error, no real help in > the forum, after banging your head for straight 8 hours you > finally know why this happens, you delete the objects with an > explicit delete and regenerate the binding objects, but the > binding table does not have a surrogate, you do that within > the same transaction. > What wouldnt pose a problem in straight JDBC because you > clear the m:n elements out of the many to many table before > setting them anew, causes hibernate to choke. > Solution, set the relational binding to lazy thus the objects > do not get marked as deleted before loading the parent object > and thus the setting works again. > > It is cases like that, which are very commmon where all the > documentation unfortunately utterly fails and where you can > sink hours into hibernate. > > Hibernate to my taste lacks a high level layer which resolves > such cases automatically, some kind of > hibernatetool.resolveManyToManyBinding(BindingList) would > have helped a lot in this case. > > Before Hibernate 2 it also was the session handling which > lacked those tools, that fortunately is resolved now. > > > > Rafael Nami wrote: > > I'm not an expert in this, but I think if you use another type of > > collection, like a Set or a List, this behavior won't > occur. I usually > > use Sets to many to many and Lists to bidirecional relations. > > > > Hope that it helps > > > > Rafael Mauricio Nami > > > > 2005/9/12, Dave <[EMAIL PROTECTED]>: > > > >>I am struggling with Hibernate 1-to-many mapping(collection). > >>Could someone tell me how to manage the collection of > one-to-many mapping? a > >>little code will be very helpful. > >> > >>I have a very simple one-to-many relationship: an Item has > many Picture(s). > >> > >>ENTITY -- Item > >>@... > >>public class item { > >>private Collection pictures; > >>private Integer id; > >> > >>// getter/setter for id and @Id(...) > >> > >> > >>@OneToMany(cascade = {CascadeType.MERGE}, fetch = FetchType.EAGER, > >>mappedBy="item") > >>public Collection getPictures() { > >>return pictures; > >>} > >> > >>public void setPictures(Collection pictures) { > >>this.pictures = pictures; > >>} > >> > >>public void addPicture(Picture p) { > >> > >>if (pictures == null) > >>pictures = new ArrayList(); > >>pictures.add(p); > >> > >>} > >>} > >> > >>ENTITY Picture -- > >>@ .... > >>public class Picture { > >>private Item item; > >>private Integer id; > >> > >>// constructor > >>public Picture(Item item, ....) { > >>this.item = item; > >>.... > >>} > >>// getter/setter for id and @Id(...) > >> > >>@ManyToOne > >>@JoinColumn(name="itemId") > >>public Item getItem() { > >>return item; > >>} > >> > >>public void setItem(Item item) { > >>this.item = item; > >>} > >>} > >> > >>I create an Item in persistence without any pictures. Then > use a session > >>bean to add pictures to the item. > >> > >>Session Bean -- > >> > >>@Stateless > >>public class ItemManagerBean implements ItemManager { > >> > >>public void addPictureToItem(Item item, Picture p) { > >>item.addPicture(p); > >>em.merge(item); > >>} > >> > >>} > >> > >>The merge() ignores those pictures that are already in persistence. > >>Add picture P1: ---> persistence: P1, ( great!) > >>Add picture P2 ---> persistence: P1, P1, P2 (P1 duplicated) > >>Add picture P3 ---> persistence: P1, P1, P2, P1, P2, P3 > >> > >>Obviously, the merge() ignored what are already in > persistence. All pictures > >>has Id. EM.merge() should be able to know P1 is already in > persistence when > >>adding P2. > >> > >>I f I do not call merge(), nothing will be persisted. > >> > >>I do this from Web GUI. Transaction is thread-based.(default) > >> > >>Do I miss anything? or Is this a Hibernate bug ? > >> > >> > >>----------------- > >> > >>I tried one thing: Create a picture in persistence using > another session > >>bean. Then use em.refresh(item). First time it works, and I > can see the > >>picture from item.getPictures(). > >>Then I create another picture the same way, and call > em.refresh(item) again, > >>but this time item.getPictures() does not have the second picture. > >>Not that I have changed the Cascade type to REFRESH. > >> > >>Basically what is the way to manage the collection in > one-to-many mapping? > >> > >>I am using JBoss 4.0.3RC1 on XP. > >> > >> Please help! Thank you. > >> > >>Dave > >> > >> > >> > >>__________________________________________________ > >>Do You Yahoo!? > >>Tired of spam? Yahoo! Mail has the best spam protection around > >>http://mail.yahoo.com > > > > > > >
