Thanks Jani, good to hear someone has gone down this road before. Since you did it in code, is there a reason you kept a sequence value on Tenant rather than using Widget.objects.aggregate(Max(Widget.sequence_value)) ? I ask because for my app, Widget is actually just one of several cases where I need this pattern. If I could keep all the book-keeping on the model with the constraint, that seems cleaner to me. But, of course, I'm not willing to pay a huge performance or corruption penalty just for vague ideological purity :)
Thanks again! ~matt On Tuesday, January 13, 2015 at 5:07:21 AM UTC-8, Jani Tiainen wrote: > > I've done something similiar. > > Only way to do that is that you need to upkeep that tenant sequence_id > manually, > > So doing something like: > > class Tenant(models.Model): > name = models.CharField(max_length=50) > sequence_value = models.IntegerField() > > and in a code: > > tenant = Tenant.object.get(id=tenant_id).select_for_update() # > Pessimistic locking > tenant.sequence_value = tenant.sequence_value + 1 > tenant.save() > > widget = Widget(owner=tenant,sequence_value=tenant.sequence_value) > widget.save() > > That should do the trick. Another option could be using table triggers to > automate > that within a database table trigger(s). > > On Mon, 12 Jan 2015 21:26:54 -0800 (PST) > Matt Cooper <[email protected] <javascript:>> wrote: > > > I'm building a multi-tenant application with a data model that > simplifies > > to: > > > > class Tenant(models.Model): > > name = models.CharField(max_length=50) > > > > class Widget(models.Model): > > owner = models.ForeignKey(Tenant) > > sequence_id = <question here> > > > > > > I want Widget.sequence_id to work like an AutoField (that is, > automatically > > give me something unique and generally incrementing by 1) but scoped to > a > > single Widget.owner. So for instance, when Tenant A creates 3 widgets, > they > > would get sequence_ids 1, 2, and 3. Then Tenant B comes along and > creates 2 > > widgets; those widgets get sequence_ids 1 and 2. The tenant/user gets no > > control over the number, but it's something she'll see in the UI. > > AutoNumber is out because from the perspective of a single tenant, they > > should have sequential widget IDs. GUIDs/UUIDs are out because it needs > to > > be human-readable. > > > > I looked through docs on AutoField and unique_together. I turned > > StackOverflow upside down and only found this > > <http://stackoverflow.com/questions/18072586/django-autofield-increment>, > > > which isn't quite what I want. I didn't see anything on > djangopackages.com > > that would solve my problem, though I could have missed it. > > > > Basically, has anyone done something like this before and have a > suggested > > pattern? > > > > Thanks! > > ~matt > > > > -- > > You received this message because you are subscribed to the Google > Groups "Django users" group. > > To unsubscribe from this group and stop receiving emails from it, send > an email to [email protected] <javascript:>. > > To post to this group, send email to [email protected] > <javascript:>. > > Visit this group at http://groups.google.com/group/django-users. > > To view this discussion on the web visit > https://groups.google.com/d/msgid/django-users/37fd32e7-28dd-4c10-8451-b0d705a3e52e%40googlegroups.com. > > > > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "Django users" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/django-users. To view this discussion on the web visit https://groups.google.com/d/msgid/django-users/1ab4b16d-df97-4412-9622-22cf3b344f80%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
