I've created a JIRA for this https://hibernate.atlassian.net/browse/OGM-1236
Thanks On Fri, Jan 13, 2017 at 2:26 PM, Sanne Grinovero <sa...@hibernate.org> wrote: > Hi Yoann, > > while you might be using a specific implementation when persisting > your new entities, when you're loading the object back from the > database how is Hibernate supposed to know > A) which implementation you want it to use > B) which order to use, if you didn't map e.g. an order column to > store the ordering information (MongoDB not needing a strategy is an > exception) > > The entity model expresses the intent of the end user, but also it > expresses its requirements which will be taken into account by ORM > when it needs to provide an implementation for the "Collection" > interface. > > A List expresses the ordering requirement by contract; if you map a > relation as "Collection" I wage you're not interested in the order, > but you're rather more interested in accepting a wide range of > implementations, some of which might ignore the ordering requirement. > By doing so, you're explicitly telling both ORM and your other code > interacting with the model that ignoring the order is acceptable. > > BTW I suspect mapping things as a generic Collection is a very unusual > (or lazy) choice; I don't remember ever using it as it's quite > ambiguous, and there's no way any specification diagram will lead you > to recommend using a Collection (other than cleanly and explicitly > wanting to express you don't care about ordering, nor other properties > like uniqueness...) > > Thanks, > Sanne > > > On 13 January 2017 at 13:29, Yoann Rodiere <yrodi...@redhat.com> wrote: >>> I think it's a reasonable expectation, as long as we're talking >>> specifically about mapping a *List* and not just a generic Collection. >> >> >> Ah, this topic again :) I know I'll be all lone, but I'll try anyway! >> >> If we do it for List, and unless there are technical issues that prevent us >> from doing so, I would be in favor of doing it for any kind of collection. >> >> In Collections, the fact that iteration order is deterministic is mostly up >> to the implementation, which is different from saying it's not >> deterministic. From the javadoc for Collection#iterator(): >> >>> There are no guarantees concerning the order in which the elements are >>> returned >>> (unless this collection is an instance of some class that provides a >>> guarantee). >> >> >> Deterministic, and even predictable order is not exclusive to List, either: >> for instance, LinkedHashSet is not a List, it has a specific iteration >> order, but there is nothing in its implemented interfaces (Collection, Set) >> that defines this order. >> >> My point is, we can't rely on the implemented interface to decide whether >> the iteration order is important or not, so we may as well decide it is >> always important. Unless there are annoying technical challenges, of course. >> >> Yoann Rodière <yrodi...@redhat.com> >> Software Engineer >> Red Hat / Hibernate NoORM Team >> >> On 13 January 2017 at 13:48, Sanne Grinovero <sa...@hibernate.org> wrote: >>> >>> I think it's a reasonable expectation, as long as we're talking >>> specifically about mapping a *List* and not just a generic Collection. >>> >>> On 13 January 2017 at 12:18, Davide D'Alto <dav...@hibernate.org> wrote: >>> > Hi, >>> > it seems that when using Collection of elements in MongoDB, users >>> > expect to have the elements in the same order as in the db. You can >>> > see the question on the forum here: >>> > >>> > https://forum.hibernate.org/viewtopic.php?f=31&t=1043903&p=2491218#p2491218 >>> > >>> > I also found this StackOverflow question: >>> > >>> > http://stackoverflow.com/questions/9013916/do-arrays-stored-in-mongodb-keep-their-order >>> > >>> > What do you think? Is it something that we should support? >>> > >>> > Cheers, >>> > Davide >>> > _______________________________________________ >>> > hibernate-dev mailing list >>> > hibernate-dev@lists.jboss.org >>> > https://lists.jboss.org/mailman/listinfo/hibernate-dev >>> _______________________________________________ >>> hibernate-dev mailing list >>> hibernate-dev@lists.jboss.org >>> https://lists.jboss.org/mailman/listinfo/hibernate-dev >> >> _______________________________________________ hibernate-dev mailing list hibernate-dev@lists.jboss.org https://lists.jboss.org/mailman/listinfo/hibernate-dev
