Why do we need list-index ??????????

kaylanx · **Posted:** Thu Nov 30, 2006 11:23 am

OK so i have 3 tables...

PRODUCT_GROUP
PRODUCT_SUBTYPE

and the many to many table...

PRODUCT_GROUP_SUBTYPE

The last table initally had 2 columns just the ids of the GROUP and SUBTYPE tables. This seemed to work perfectly well if i wanted to use sets, but didn't work at all if i wanted to use lists, as a list requires a list-index or index. WHY???

We want to use lists in our code not sets, so to get around this problem I added another column to the PRODUCT_GROUP_SUBTYPE table called PRODUCT_GROUP_SUBTYPE_ID and it just has the values 1..n (i.e. first row it's 1, 2nd row it's 2, nth row it's n)

I set the list index to this column, and all of a sudden it works....Why do I need this column???

here's the mapping...

Code:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="com.hidden.value.ProductGroupValue" table="product_group">
        <id name="productGroupId" column="PRODUCT_GROUP_ID" unsaved-value="0"/>
        <property name="description" column="DESCRIPTION"/>
        <property name="roleId" column="ROLE"/>
        <list name="productSubTypes" table="product_group_subtype">
            <key column="product_group_id"/>
            <list-index column="product_group_subtype_id"/>
            <many-to-many class="com.hidden.value.ProductSubTypeValue" column="product_subtype_id"/>
        </list>
    </class>
</hibernate-mapping>

It all works ok now, but just puzzled on why i should need to add the extra column??????

cheers

Andy.

wykoff · **Posted:** Thu Nov 30, 2006 11:37 am

did you read "understanding collection performance" in chapter 19.5 of the reference guide?

kaylanx · **Posted:** Thu Nov 30, 2006 11:49 am

wykoff wrote:

did you read "understanding collection performance" in chapter 19.5 of the reference guide?

No need to be like that......I was only asking a simple question!!!!!!!!!

No I hadn't, I've just had a quick look and it seems to make sense. Although it is still pointless in my case as the group and subtype tables contain static data and won't be updated via hibernate, only read from.

Andy

lester · **Posted:** Thu Nov 30, 2006 12:00 pm

Because List implies ordering of its elements. 'list-index' or 'index' elements defines that order. If you don't need the order, you may use bag, which defines List with Bag semantic (no guarantee about order).

kaylanx · **Posted:** Thu Nov 30, 2006 12:12 pm

lester wrote:

Because List implies ordering of its elements. 'list-index' or 'index' elements defines that order. If you don't need the order, you may use bag, which defines List with Bag semantic (no guarantee about order).

Thank you!!! thats perfect!!!

Cheers

Andy

wykoff · **Posted:** Thu Nov 30, 2006 12:16 pm

kaylanx wrote:

No need to be like that......I was only asking a simple question!!!!!!!!
Andy

Actually, I wasn't being snide! I simply didn't know if you had read it and it still didn't make sense or if you hadn't yet found that part of the reference.