Hibernate version: 3.0.5

I have read the documentation regarding indexed collections, but I have
not found (in the reference manual at least) an answer to several
questions about managing list collections with Hibernate:

0. Does the list index column need to also be a property of the child
object, or does it only need to be declared as a column in the db?

1. Does Hibernate compute the list index for a list element? I am not
clear on what happens when, for example the object containing a
list is loaded, and presumably the list itself is only lazily loaded, and
then an item is added to the list or inserted in the middle - who's
responsible for making sure the list stays consistent?

2. When/where does this happen if Hibernate does compute the list
index? Does this happen when flushing new objects?


3. One solution I've seen for managing the list index is presented in
http://www.hibernate.org/193.html However, there are several
questions I have regarding this:

a. A performance/efficiency issue: what happens when the list gets large
(100's or 1000's of items) and the 'getIndex()' is being called?
In particular is the list is initialised lazily and list items are
retrieved as they are being accessed. Is this a price that needs to
be paid or is this not an issue?

b. What if the index column is something that consitutes part of the
natural key (something like order line number) - when retrieving
the element index value, the solution uses the 'indexOf' method on
the parent object's list, which uses the 'equals' method, causing
infinite recursion. How does one avoid this?

Thanks in advance for any assistance here.[/list]

0.

Not unless inverse="true". It is possible to have a unidirectional one-to-many list in HB3. This is better explained in the (unpublished) HB3.1 docs.

1.

I don't quite follow. If foo = list.get(3) then 3 is the index of foo.

2.

Whenever the collection is flushed. Yes, you can rearrange elements and HB will update things correctly.

3.

This is obsolete stuff that referred to HB2.


Caveat: We DO NOT recommend lists as a good thing to use in data modelling. Professional data modellers do not use such inelegant constructs.

Hi Gavin,



What do you recommend instead of a list for an ordered collection attached to an object? eg I have an object with a set of filters associated with it, and those filters need to be kept in order.

cheers,

David

You should order things by truly *meaningful* information.

eg. use a set with order-by="createdDateTime"

Have you solved your problem ?
I need the same solution.
Can you post the mapping file and the java code ?
Thank you very much.

Gavin,

First thanks for the informative reply. I'm looking forwards to seeing the
new doc version.

However, I've got another query related to your quotes below:





I need to be able to perform both actions - the ordered set of items
needs to be kept with the same order every time it is accessed,
and when being updated, the relative position of items in the list should
reflect the modified state (For the first case, imagine a stack that may
need to be popped, but until it happens the order cannot change; the
second case may involve the same 'stack' with the ability to remove
things in the middle).

What would the correct Hibernate construct/s to implement
these requirements be?

And if these need to be implemented using a list in Hibernate 3,
is my question 3 below still valid?