Hi Shai, Thanks for your feedback.
Our 'real' use case, is we have an opaque legacy application that we are rewriting in Django. Adding columns to the tables before we have migrated it away from the old application is too risky to do. I'm at the PyCon2017 sprins now, and as JKM said it -- having to deal with non-primary-key databases might be due to poor life choices :-). I agree that non-uniqueness is an antipattern -- my argument is purely about what systems the ORM can interract with/support rather than a feature that would/should be used to build new applications/models. I would hope that just like with RawSQL or @csrf_exempt, docs would make that clear. The huge value we get even without get() or admin/etc is making multi-join queries super-easy through the amazing queryset api. I'm not very familiar with the Meta API formalization, so maybe you could elaborate how we would use it in such a circumstance -- would I somehow be setting _meta = CustomThing() the way we add model managers by setting objects? Would that work on the same backend/db connection? I originally feared that removing PK would be a complex and burdensome project -- which is why I have been content with hacks until now. As I've found preliminarily, pk is not as bound as I thought. This is mostly because unsaved model objects are already possible, so a lot of code already tests for model.pk before doing something with it. I was also surprised to see, e.g. db.migrations doesn't seem like it would need any changes at all. To go back to use-cases, and the relation to composite fields, a lot of our keyless tables seem to be about set membership. Most of these *are* basically elaborate many-to-many intermediate tables, where two (or three) fields link several tables together as connected. When we have those multiple ids, I have been using models.ForeignObject to make ORM links. One is something like: class Vote(models.Model): list = models.ForeignKey("List") user = models.ForeignKey(User) ## a bunch of other fields comment = models.ForeignObject("VoteComment", on_delete=models.CASCADE, from_fields=['list_id', 'user_id'], to_fields=['list_id', 'user_id']) I know ForeignObject isn't an externally supported API. However, I think it does gesture how composite foreignkeys would emerge from this. The first step is to get rid of places that depend on a (unique and singular) primary key -- from there, we can (even slowly) add support for a ForeignKey pointing to an object without a primary key but does have the same unique_together field coupling. Once we support ForeignKey() that way, we can work on support for inheritance and admin support. /sky On Tuesday, May 23, 2017 at 4:31:47 AM UTC-4, Shai Berger wrote: > > Hi, > > Thank you for making this suggestion. > > It is my guess that allowing pk-less models will place quite a burden on > many > parts of Django, which assume a PK exists. There may also be other > solutions > to the problem you raise -- e.g. changing the legacy table to add a PK, > perhaps while providing a pk-less view to any legacy systems which need to > access it. > > In general, SQL database tables without any uniqueness guarantee are an > antipattern, which I don't believe Django should support. The question > remains > how much such a feature can be made to contribute towards composite keys. > > All in all, I would like to know more about your use case -- if you are > going > to have no get/delete, no Admin, no updating save, how exactly are you > going > to use these models? As you may be aware, since the Meta API > formalization, it > is possible to create pseudo-models which are good enough for many > purposes, > without changing Django and with much less strict adherence to "real" > models' > behavior. Perhaps that is the way to go? > > HTH, > Shai. > > On Monday 22 May 2017 21:50:07 sky.d...@moveon.org <javascript:> wrote: > > Hi, > > > > We have several legacy database tables that don't have primary keys. > With > > older versions of Django, we've hacked it by lying about a field that > was > > not a primary key but recent Django versions validate pks more strictly. > > > > Some (but not all) of our legacy tables have multiple primary keys -- > i.e. > > are unique only across a few fields. This harks to the CompositeField > work > > and discussion [0]. > > > > But CompositeFields are not enough for us, some of our tables are > > essentially append-only, and have no uniqueness constraints across > any/all > > fields. It also seems like CompositeField has stalled several times > > precisely because we are spiking to a very complex end goal. > > > > I'd like to propose, both as an incremental step to CompositeFields and > > something useful in itself, a model Meta option for > `without_primary_key` > > -- if Meta.without_primary_key=True then it would turn off the > complaints > > during model validation, etc. One might object that things like > > get/delete/caching can't work with that model. However those features > > can't be supported in tables without a primary key anyway. > > > > Incrementally, after without_primary_key is implemented/supported, we > could > > then add features for models without_primary_key but also has a > > Meta.unique_together value across some fields -- i.e. start trying to > > support inheritance and/or ForeignKey references to those tables, > building > > up support. > > > > I've started looking at how deep a change this would be, and believe > it's > > pretty tractable. > > Before I get too involved with a DEP and PR, what do people think? > > > > /sky > > > > [0] Most recent thread: > > > https://groups.google.com/forum/#!searchin/django-developers/primary$20keys > > |sort:date/django-developers/wakEPFMPiyQ/ke5OwgOPAQAJ > -- You received this message because you are subscribed to the Google Groups "Django developers (Contributions to Django itself)" group. 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