inverse attribute - too confusing !!!

[Sandeep Vaid]

If we have a bidirectional association - we need to make one end of the association as inverse.

Consider example of Item - Bid bidirectional association where
From Item to Bid it's one-to-many association
From Bid to Item it's many-to-one association

In Hibernate_Reference : It's mentioned as :
All bi-directional associations need one side as inverse. In a one-to-many association it has to be the many-side.

According to this, the inverse attribute should be @ Bid side. This means we need to specify inverse attribute in Bid.hbm.xml file.

BUT (NOTE THE CONTRADICTION)

In Hibernate In Action Book, it's written in Item.hbm.xml as :

<class
name="Item"
table="ITEM">
...
<set
name="bids"
inverse="true">
<key column="ITEM_ID"/>
<one-to-many class="Bid"/>
</set>
</class>

The following are few more related questions :
1. When we say many side of association (Bid) do we mean/refer to Bid.hbm.xml ?

2. Does this mean that, if i specify the inverse attribute in Item.hbm.xml (i.e Item Side [One Side of association]), it means ignore the changes made @ item say. Hence if we only call item.getBids().add(bid), no changes
will be made persistent. Instead we are telling Hibernate that it should propagate changes made at the Bid end of the association to the database. i.e when we call bid1.setItem(item) ,it should become persistent ?

[Jaikiran Pai]

This has a very good explanation on inverse attribute of Hibernate.

[Sandeep Vaid]

Jaikiran, the link provided by you is really a nice one. but sill i have few doubts :

In case of Item -> Bid Bidirectional Association

Item.hbm.xml

 <!--  Item - Bid Association - One-to-Many -->
   <set name="bids" 
   inverse="true"
   cascade="all-delete-orphan"> 
   <key column="ITEM_ID" />
   <one-to-many class="Bid"/>
   </set>

Item.java

public void addBid(Bid bid)
{
  System.out.println("Inside addBid(Bid bid)");
  bid.setItem(this);
 this.bids.add(bid);
}
    

Can you please justify the output in the following cases :
Case 1:
inverse="true"
bid.setItem(this);
RESULT : No Error. No INERST statement

Case 2:
inverse="false"
bid.setItem(this);
RESULT : No Error. No INERST statement

Case 3:
inverse="true"
this.bids.add(bid);
RESULT : Exception in thread "main" org.hibernate.PropertyValueException: not-null property references a null or transient value: Bid.item

Case 4:

inverse="false"
this.bids.add(bid);
RESULT : Exception in thread "main" org.hibernate.PropertyValueException: not-null property references a null or transient value: Bid.item
[ August 27, 2007: Message edited by: Sandeep Vaid ]

[Jaikiran Pai]

Sandeep, could you please post the entire exception stacktrace that you are seeing. Also, please post the hbm mapping for your Bid which contains the many-to-one declaration. The other information that will help is the code where you are saving/updating the Item or Bid object.

P.S: I am travelling tonight and wont be able to access JavaRanch. Once you post these details, either someone else will be able to explain you more or you will probably see my reply in a couple of days. So please be patient