Hi Thomas, Thanks for your explanations. A couple of follow-up questions...
> > -----Original Message----- > From: Thomas Mahler [mailto:[EMAIL PROTECTED] > Sent: maandag 16 juni 2003 21:46 > To: OJB Users List > Subject: Re: Questions re. mapping of associations... > > > Hi Tim. > > Leeuw van der, Tim wrote: > > Hello, > > > > I'm trying to convert my existing JDO-metadata mappings to an OJB > > repository.xml ... > > [...] > > I couldn't find anywhere the use of such anonymous mappings. > > It's a relatively new feature and the is not available with RC3 or on > the Website, but it is already in CVS: > http://cvs.apache.org/viewcvs/db-ojb/xdocs/howto-use-anonymous-keys.xml > add the file to the xdocs folder of the source distro and execute the > ant target "xslt" and ready is your complete html docu on this topic ! > When you say that it's not available in RC3, do you mean that the documentation for it is not available in RC3? Or does the feature itself not work yet in RC3? > > > > Another thing which is: With JDO, I defined several java.util.List > fields > > and specified that they should be stored/retrieved in order. I > really need > > to maintain the order of elements in the list, but I would prefer > not to > > have to manually do that housekeeping. > > you can use the collection-descriptor attributes orderby and sort to > maintain order: > The orderby attribute may specify a field of the element class. The > Collection or Array will be sorted according to the specified > attribute. > The sort attribute may be used to specify ascending or descending > order > for this operation. > > > > Do I have to explicitly use odmg.DList in my code? Similar for a > > java.util.Map; do I have to explicitly use odmg.DMap? > > Mhh, what do you want to achieve? using the ODMG persistent > collections > does not make much sense in JDO (may be I'm missing something). > Sorry for confusing you here. I have some existing mappings for JDO but I will need to use OJB instead, achieving similar results. So I won't be using JDO anymore, for the moment at least. With JDO I could use a plain java.util.List and tell the JDO implementation to maintain for me the order of elements so that I read them in the same order as I put them in the list. I looked at the order-by attribute of the reference descriptor, but I can't use that. There is no attribute in my element-classes that I can sort on; it's the order that I put them in the list that is relevant. My domain-model is a sort of graph, where each node in the graph has links to multiple other nodes. I could potentially add a sequence-number attribute to maintain order of the nodes for their ancestor. However, I also need to store a path over this graph, and each node can be part of an unlimited number of paths. A node can even appear multiple times in the same path. I need an indirection-table therefore, and my sequence-number needs to go into the indicrection-table. It would be horribly inconvenient to have to decompose the n:m mapping manually in source. Therefore my question: With JDO I can achieve this with any implementation of the java.util.List interface that I find convenient. Is the only way that I can achieve this with OJB by using org.odmg.DList? And if I want to store a java.util.Map in the database, does it have to be a org.odmg.DMap instance? I want to be sure of this before I change my code and dive into how to use those things... I'm still in the stage of trying to find my way with OJB. > cheers, > thomas > > > > > With regards, > > > > --Tim van der Leeuw > > > > > > Thanks a lot, --Tim van der Leeuw --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
