Yep. The IDUtil-returned sequence is not an RFC-compliant UUID. It is kind of our own invention. We can change it to a formal UUID. Though Java still doesn't support UUIDv7, which is bummer. Wonder how easy is is to write a UUIDv7 generator on our own?
While we are on this topic, my pet peeve about PK generation is the opaque "Cayenne-Generated" strategy in the Modeler. Its original motivation was to dynamically provide an optimal strategy for a specific database, considering widely differing DB capabilities. Now all databases can do everything, so this strategy is just confusing. It should be expanded into a list of specific strategies (PK table, PK procedure, PK sequence, UUID). Each one can have its own implementation per DbAdapter. Andrus > On Aug 26, 2024, at 7:24 AM, Jurgen Doll <jur...@ivoryemr.co.za> wrote: > > Hi Michael > > So Cayenne actually currently does support generating UUID PK's, if in the > Cayenne Modeler you: > > 1. set your column type to BINARY > 2. set it to a length of 16 > 3. check the PK flag, and > 4. set the table's "PK Generation Strategy" to Cayenne > > This will result in a UUID being generated via > "org.apache.cayenne.util.IDUtil.pseudoUniqueSecureByteSequence(int)". > > Unfortunately this UUID is currently a MD5 digest which is bad for indexing. > > The reason for the digest is to anonymise the underlying UUID which is 16 > bytes long consisting of: > bytes 0..3 - incrementing # > bytes 4..11 - timestamp > bytes 12..15 - IP address > > The above UUID generation could easily be changed to use Java's native UUID > which is a Time-Based UUID that would be index friendly, if I'm not mistaken. > > Regards > Jurgen > > > On Sat, 24 Aug 2024 04:42:39 +0200, Michael Gentry <blackn...@gmail.com> > wrote: > >> Hi Andrus, >> >> Part of what I meant by adding UUID support to Cayenne was to include UUID >> as a PK mechanism in Cayenne modeler and provide a corresponding PK >> generator class. Nothing currently stops you from manually setting a UUID >> yourself, but including support in the modeler would be a more natural fit, >> I think. >> >> Thanks, >> mrg >> >> >> On Fri, Aug 23, 2024 at 4:33 PM Andrus Adamchik <aadamc...@gmail.com> wrote: >> >>> I am actually glad we went on a tangent and started discussing UUIDs. I >>> just ran into a use-case of an idempotent PUT API endpoint that takes a mix >>> of new and existing objects, and there's no natural key in the entity to >>> check whether new (PK-less) objects are already in DB (so that we UPDATE >>> them instead of INSERT). UUID would come in handy in this situation :) >>> >>> (FWIW, the endpoint is running on Agrest with Cayenne underneath, and >>> Agrest is the layer that ensures idempotent semantics). >>> >>> Andrus >>> >>> >>> > On Aug 20, 2024, at 12:01 PM, Hugi Thordarson <h...@godurkodi.is> wrote: >>> > >>> > Judging from some very, very basic experimentation, Cayenne seems to do >>> fine with UUID PKs. >>> > >>> > Db generated UUIDs really just work like serial integers with a >>> different generated value type: >>> > >>> > >>> https://github.com/hugithordarson/xx-c42/blob/main/src/main/java/family/MainUUIDDbGenerated.java >>> > >>> > …and the fun stuff, app generated UUID PKs (for all your cross- back- >>> and forth-referencing insertion needs) look fine as well: >>> > >>> > >>> https://github.com/hugithordarson/xx-c42/blob/main/src/main/java/family/MainUUIDAppGenerated.java >>> > >>> > …although I wouldn't vouch for that PK-generation method of exposing the >>> PK and populating it in a post-add hook. >>> > >>> > Unfortunately h2 doesn't appear to support deferred constraints, but I >>> tested this against postgres with the constraints present. >>> > >>> > Anyway, pardon this tangent, born from a joke. I won't really say this >>> really demonstrates much, but it was at least a fun experiment over lunch >>> and thought you might enjoy it:). >>> > >>> > Cheers, >>> > - hugi >>> > >>> > >>> >> On 16 Aug 2024, at 17:26, Michael Gentry <blackn...@gmail.com> wrote: >>> >> >>> >> If UUID PKs are really going to be a thing, we should probably add them >>> to >>> >> Cayenne... >>> >> >>> >> >>> >> On Fri, Aug 16, 2024 at 9:44 AM Hugi Thordarson <h...@godurkodi.is> >>> wrote: >>> >> >>> >>> Hi Michael! >>> >>> >>> >>> Sure, the UUID comment was meant as a bad joke, my world is all DB >>> >>> generated integer keys. >>> >>> >>> >>> That being said, I've wanted to try out UUID keys for a while. Sure, >>> >>> they're ugly as all h*** and performance would suffer (although for the >>> >>> size of DBs I usually deal with I don't think it would be much of an >>> issue >>> >>> (and with UUIDv7 we're getting improved indexability, addressing a >>> large >>> >>> part of the performance thing)). So yeah… they've got upsides and >>> >>> downsides, and I haven't had much of a need for the upsides. But I've >>> got a >>> >>> suspicion they might sneak into common use soon. Perhaps when >>> >>> openai.com/gptbot <http://openai.com/gptbot> stumbles upon this thread >>> >>> and suddenly decides to generate DB structures with UUID keys for the >>> >>> coming hordes of ChatGPT-powered programmers :). >>> >>> >>> >>> Cheers, >>> >>> - hugi >>> >>> >>> >>> >>> >>>> On 16 Aug 2024, at 14:20, Michael Gentry <blackn...@gmail.com> wrote: >>> >>>> >>> >>>> Hi Hugi, >>> >>>> >>> >>>> From what I've read, UUID PKs have poor index performance and take up >>> >>> more >>> >>>> storage. >>> >>>> >>> >>>> Wouldn't it be better to use an integer sequence like PostgreSQL and >>> >>> Oracle >>> >>>> support? You can generate your PKs up front and Cayenne already knows >>> how >>> >>>> to deal with them. >>> >>>> >>> >>>> Thanks, >>> >>>> mrg >>> >>>> >>> >>>> >>> >>>> On Thu, Aug 15, 2024 at 6:49 AM Hugi Thordarson <h...@godurkodi.is> >>> >>> wrote: >>> >>>> >>> >>>>> Hi Nikita, >>> >>>>> >>> >>>>> again, thanks for looking into this! And yeah, totally understand how >>> >>>>> we're not about to insert everything in one commit. Well, at least >>> until >>> >>>>> the universe decides it's time everyone move to app generated UUID >>> PKs >>> >>> and >>> >>>>> deferred constraint checks :). >>> >>>>> >>> >>>>> Cheers, >>> >>>>> - hugi >>> >>>>> >>> >>>>> >>> >>>>> >>> >>>>>> On 14 Aug 2024, at 11:27, Nikita Timofeev < >>> ntimof...@objectstyle.com> >>> >>>>> wrote: >>> >>>>>> >>> >>>>>> In this case it seems like a true cycle, the Person entity has two >>> >>>>>> relationships to self. And that particular case Cayenne didn't >>> handle >>> >>>>> well >>> >>>>>> historically. >>> >>>>>> But looking at it, I want to try and tweak the new Graph-based >>> sorter, >>> >>>>>> because two updates generated shouldn't depend on each other. So >>> maybe >>> >>> it >>> >>>>>> could be fixed now. >>> >>>>>> It still won't be able to insert all the data in one go though. >>> >>>>>> >>> >>>>>> On Wed, Aug 14, 2024 at 11:33 AM Hugi Thordarson <h...@godurkodi.is >>> > >>> >>>>> wrote: >>> >>>>>> >>> >>>>>>> Hi again Nikita! >>> >>>>>>> >>> >>>>>>> saw the fix you made yesterday and it works great for the test I >>> >>>>> created, >>> >>>>>>> so thanks for that! >>> >>>>>>> >>> >>>>>>> However, turns out that for the more complex case in our actual >>> >>> project, >>> >>>>>>> the operation still fails. >>> >>>>>>> I've added a new example to the test project that models that case >>> a >>> >>>>>>> little more closely: >>> >>>>>>> >>> >>>>>>> >>> >>>>>>> >>> >>>>> >>> >>> >>> https://github.com/hugithordarson/xx-c42/blob/main/src/main/java/family/MainWithAddedBackReference.java >>> >>>>>>> >>> >>>>>>> Any thoughts? >>> >>>>>>> >>> >>>>>>> Cheers, >>> >>>>>>> - hugi >>> >>>>>>> >>> >>>>>>> >>> >>>>>>> >>> >>>>>>>> On 12 Aug 2024, at 13:52, Nikita Timofeev < >>> ntimof...@objectstyle.com >>> >>>> >>> >>>>>>> wrote: >>> >>>>>>>> >>> >>>>>>>> Hi Hugi, >>> >>>>>>>> >>> >>>>>>>> Thanks for the perfect example, that's always my main problem. >>> >>>>>>>> I've found the issue with the new flush logic [1]. The last >>> operation >>> >>>>>>>> creates two logical changes (DbRowOps), and one of them is later >>> >>>>>>> discarded >>> >>>>>>>> as there's nothing to flush to the DB. >>> >>>>>>>> However it's discarded only after the sorting, so it fails. >>> >>>>>>>> I'm already testing a fix for that. >>> >>>>>>>> >>> >>>>>>>> Also wanted to mention that in this exact case >>> >>> GraphBasedDbRowOpSorter >>> >>>>>>>> helps, as it checks operation internals and ignores it. >>> >>>>>>>> >>> >>>>>>>> [1] https://issues.apache.org/jira/browse/CAY-2866 >>> >>>>>>>> >>> >>>>>>>> On Fri, Aug 9, 2024 at 12:58 PM Hugi Thordarson < >>> h...@godurkodi.is> >>> >>>>>>> wrote: >>> >>>>>>>> >>> >>>>>>>>> Hi Andrus, >>> >>>>>>>>> I've been taking a look at this with Maik, here's a runnable >>> example >>> >>>>>>>>> project containing a commit that works on v4.1 but fails in v4.2: >>> >>>>>>>>> >>> >>>>>>>>> https://github.com/hugithordarson/xx-c42/ >>> >>>>>>>>> >>> >>>>>>>>> Quick link to the code actually demonstrating the failure: >>> >>>>>>>>> >>> >>>>>>>>> >>> >>>>>>> >>> >>>>> >>> >>> >>> https://github.com/hugithordarson/xx-c42/blob/main/src/main/java/family/Main.java >>> >>>>>>>>> >>> >>>>>>>>> The last commit certainly results in a circular reference being >>> >>>>> present >>> >>>>>>> in >>> >>>>>>>>> the object graph, but it probably shouldn't be a problem for the >>> >>>>> actual >>> >>>>>>>>> operation since we're only updating a single row, right? >>> >>>>>>>>> >>> >>>>>>>>> Cheers, >>> >>>>>>>>> - hugi >>> >>>>>>>>> >>> >>>>>>>>> >>> >>>>>>>>> >>> >>>>>>>>> >>> >>>>>>>>> >>> >>>>>>>>> >>> >>>>>>>>>> On 8 Aug 2024, at 18:10, Andrus Adamchik <aadamc...@gmail.com> >>> >>>>> wrote: >>> >>>>>>>>>> >>> >>>>>>>>>> Hi Maik, >>> >>>>>>>>>> >>> >>>>>>>>>> Could you provide an example of a failing graph? >>> >>>>>>>>>> >>> >>>>>>>>>> Thanks, >>> >>>>>>>>>> Andrus >>> >>>>>>>>>> >>> >>>>>>>>>>> On Aug 7, 2024, at 7:31 AM, Maik Musall <m...@selbstdenker.ag> >>> >>>>> wrote: >>> >>>>>>>>>>> >>> >>>>>>>>>>> Hi everyone, >>> >>>>>>>>>>> >>> >>>>>>>>>>> we upgraded an application from Cayenne 4.1.1 to 4.2.1, and now >>> >>>>> we’re >>> >>>>>>>>> getting more cyclic graph errors from AshwoodEntitySorter. Years >>> >>> back >>> >>>>> we >>> >>>>>>>>> already had a similar problem, but @SortWeight didn’t help and >>> >>>>>>>>> GraphBasedDbRowOpSorter wasn’t ready. The latter is now in 4.2 >>> >>> stable >>> >>>>>>> but >>> >>>>>>>>> fails to save even simpler graphs, so unfortunately not a >>> solution. >>> >>> We >>> >>>>>>> had >>> >>>>>>>>> been able to get stable operation by fetching PK’s from >>> PostgreSQL >>> >>>>>>>>> sequences (Oracle-style) instead of having Cayenne generate them, >>> >>> and >>> >>>>>>> lived >>> >>>>>>>>> with the performance penalty associated with that, but the >>> problem >>> >>>>> came >>> >>>>>>>>> back with 4.2 despite that. Not reliably reproducible though, >>> >>> happens >>> >>>>>>> every >>> >>>>>>>>> now and then. Any thoughts? >>> >>>>>>>>>>> >>> >>>>>>>>>>> Thanks >>> >>>>>>>>>>> Maik >>> >>>>>>>>>>> >>> >>>>>>>>>> >>> >>>>>>>>> >>> >>>>>>>>> >>> >>>>>>>> >>> >>>>>>>> -- >>> >>>>>>>> Best regards, >>> >>>>>>>> Nikita Timofeev >>> >>>>>>> >>> >>>>>>> >>> >>>>>> >>> >>>>>> -- >>> >>>>>> Best regards, >>> >>>>>> Nikita Timofeev >>> >>>>> >>> >>>>> >>> >>> >>> >>> >>> > >>> >>> > > > -- > Using Opera's mail client: http://www.opera.com/mail/
