What is the meaning of index?

fafnir · **Joined:** Wed Dec 03, 2003 9:41 pm **Posts:** 87

Sample:

Code:

<list name="carComponents" table="car_components">
    <key column="car_id"/>
    <index column="posn"/>
    <composite-element class="com.illflow.CarComponent">
            <property name="price" type="float"/>
            <property name="type" type="com.illflow.ComponentType"/>
            <property name="serialNumber" column="serial_no" type="string"/>
    </composite-element>
</list>

"car_id" is the foreign key column name. "posn" is which column name? I don't understand it.

anthony · **Posted:** Wed Feb 25, 2004 7:43 am

the collection will be ordered by posn

emmanuel · **Posted:** Wed Feb 25, 2004 8:56 am

delpouve wrote:

the collection will be ordered by posn

Even more, the collection will be indexed by posn

fafnir · **Joined:** Wed Dec 03, 2003 9:41 pm **Posts:** 87

e.g.

Code:

Parent table:
id, name
Child table:
id, parent_id, child_name

parent_id is <key column="parent_id"/>
which column is "posn"?

steve · **Posted:** Thu Feb 26, 2004 12:20 am

I would guess none, but you know your schema better than me.

Seriously, I think you just did not fully read the documentation regarding hibernate collections, specifically the list mapping. In the java2 collection farmework, the java.util.List interface defines a contract for a ollection in which all the elements of that collection are positionally indexed. In other word, in a List impl order does matter. Hibernate takes this to heart and thus you must specify how the elements are to be ordered.

In short it is mostly likely not a <list> mapping you want, but rather a <set> or <bag>. Please read the docs regarding mapping of collections.