Hey,
Here are my two cents. The biggest obstacle with Hibernate is figuring out
how to correctly map the stupid collections and relationships that are
modeled in your object model. I did not take the time to look at all your
code but maybe this will help you out:
Simple situation. You have a class say CarItem and it has an ArrayList of
CarPictures.
Hibernate requirements for mapping collections:
The collection must be an interface. The two most common ones you will use
is either a list or a set. A set garunetess that objects in its collection
are unique, however and kind of annoyinng a set does not gaurnetee or
preserve the order of objects that you add to it. A list does.
Back to the example, writing the java objects is the easy part.
CarItem() {
List carPictures = new ArrayList();
etc...
}
now we want to create a hibernate mapping file for this...
its a list so we use the list element off the of the root .hbm config
element.
Create a list with the name attribute equal to the collection interface
property name.
<list name="carItesm" lazy="false" cascade="all">
<key>
<column name="metaObjectID" />
</key>
<!-- key is importnat because the name attribute has to point to the unique
id of the "many side" of your relationship (in this case the car item has
many car
pictures, so this attribute becomes a foriegn key in the CarPicture table
because it has to to know what car item it belongs to) -->
<one-to-many class="com.yoursomedayprofitablecompany.hopefully.CarPicture"/>
</list>
Wow the more I think about this the more I realize I'm rewriting whats in
the doucmentation. I was just there yesterday go to
http://www.hibernate.org/hib_docs/v3/reference/en/html/collections.html and
setup the examples in your dev environment, its not rocket science once you
get it you'll feel on top of your world. - Duncan
----- Original Message -----
From: "Rafael Nami" <[EMAIL PROTECTED]>
To: "MyFaces Discussion" <[email protected]>
Sent: Monday, September 12, 2005 8:31 PM
Subject: Re: Hibernate: 1-to-many --> struggling
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
--
Java - Assim no Server como no Palm
<i>Java - thus in the Server as it is in Palm
