[OJB-developers] Re: MtoN-followup

[Jakob B. <jbr...@ho...>]

hi georg,

> Up to the last release this was possible, but now the entire MtoN-code
> has been changed. Now an object A can have a collection of objects B,
> but at the same time object B has to have a collection of objects A,
> effectively linking A and B tightly together. If you want to have object
> A to be part of a collection in an object C, you have to provide a
> collection in object B pointing to objects C .....

yes that's true the relationship has to be bidirectional.
i had long discussions with oleg nitz and we both came to this conclusion.
but i see that tight coupling can be a problem.

jakob

----- Original Message -----
From: "Georg Schneider" <ge...@me...>
To: "Mahler Thomas" <tho...@it...>
Cc: <jbr...@ho...>; <obj...@li...>
Sent: Thursday, June 06, 2002 1:50 PM
Subject: MtoN-followup


> Hi Jacob and Thomas
>
> This is the follow-up to my previous mail talking about the
> M:N-Relationship issue:
>
> OK, the basic issue is, that an object should be able to form part of
> different collections. The basic example I give is that you could have
> an Inventory object which contains a list of Articles, and ShoppingCart
> objects which also contain a list of Articles.
> I don't think that this is a minor feature, but it is simply the way
> objects can be used in Java.
>
> Up to the last release this was possible, but now the entire MtoN-code
> has been changed. Now an object A can have a collection of objects B,
> but at the same time object B has to have a collection of objects A,
> effectively linking A and B tightly together. If you want to have object
> A to be part of a collection in an object C, you have to provide a
> collection in object B pointing to objects C .....
>
> Object B shouldn't have to know that it is part of a collection in an
> M:N scenario.
>
> The only testcase for that MtoN-issue is testMNLoading() in MtoNMapping
> which uses the Person-Project relationship, where Person has a
> collection of Projects and Project has a collection of Persons.
>
> I have assembled a testcase which should check the form of
> MtoN-relationships where the N-Class doesn't have a collection of
> M-Objects. Of course it fails right away, but it would be a starting
> point to analyze how to fix things.
>
> I have attached the following things:
>
> 1.) a method testMultipleMtoNRelations() which should go into the
>     MtoNMapping.java file
>
> 2.) the files Inventory.java and ShoppingCart.java which go into the same
> directory
>
> 3.) the mapping for both classes which has to be added to
> repository_junit.xml
>
> 4.) the create statement for the tables and indirection tables which has
> to go into db-setup.sql
>
> Cheers
>
> Georg
>