I have a collection of a Set that works fine, but when I convert it to a List it throws a NP Exception when iterating over the objects. Dubugging it it looks like the Object is good and well until I cast it with the Iterator.next(). I am using H2-Beta4. Here are my mappings:

WORKS:
-----------

<set name="inventoryHistories" cascade="all" lazy="true">
<key column="product_id"/>
<one-to-many class="com.ldi.db.hibernate.InventoryHistory"/>
</set>

DOESN'T WORK
-------------------

<list name="inventoryHistories" cascade="all" lazy="true">
<key column="product_id"/>
<index column="inventory_history_id"/>
<one-to-many class="com.ldi.db.hibernate.InventoryHistory"/>
</list>

TEST CODE
--------------

Product p = (Product) s.load(Product.class, new Integer(1205));

assertNotNull(p.getInventoryHistories());
assertTrue(p.getInventoryHistories().size() > 0);

Iterator it = p.getInventoryHistories().iterator();
while ( it.hasNext() )
{
InventoryHistory ih = (InventoryHistory) it.next();
assertNotNull(ih); <--- FAILS
}



I know it's gotta be something simple, I have been staring at it too long. Any help is appreciated. Thanks.

Matt

I notice that you are trying to use inventory_history_id as the index of the List. I'm going to further guess that inventory_history_id is the PK into the InventoryHistory class. Thats not the purpose of the index attribute on list. The index attribute specifies property Hibernate should use to position the items within the List. So you are most likely experiencing "gaps" within your List.

Steve:

How correct you are. Thanks. Quick question if you have time, does the index column have to be a number, can it be a date? I am trying to convert a legacy system and the only thing I can order_by is the create_Date but that does not seem to be working. Thanks.

Matt

Well it has to be a int to satisfy the java.util.List contract.

Another thought is that that index element accepts a type attribute. You might try a UserType impl. The issue is that the index values need to be sequential ints for the given relation

Howdy,

It appears that all the docs on using Lists I've seen say that the index property in the mapping file is supposed to be a column name. But above you say it's supposed to be a property name. While I realize that properties map to columns, I guess I'm finding this confusing.

Is the mapping files <index column="x"/> supposed to describe the actual column name in the "child" table or is it meant to be the name of a property that manages an index value for the child class?

Thanks!

Gerry

Actually, I think I've answered my question - the column= is in fact the name of the column in the "child" table that the index is in.

I think what was throwing me was that I expected hibernate to completely manage this column and I now beleive it doesn't.

From what I'm reading, the column is used in a read-only fashion by hibernate. You have to insure the correct value is in the column. Hibernate will not populate it when saving out the parent with the List collection in it.

Is this a fair assessment of Lists and the column= attribute in the mapping file?

This is correct iff inverse="true".

Thanks - I'm starting to get most of this now :-)