There's general interest in having support for composite keys and composite foreign key. It's just that nobody has implemented it.
There are proposals among the DEPs that layout ideas how they could be implemented: - https://github.com/django/deps/blob/master/draft/0191-composite-fields.rst - https://github.com/django/deps/blob/master/draft/0192-standalone-composite-fields.rst On Mon, Feb 18, 2019, at 9:28 AM, 'Ellinghaus, Lance J' via Django users wrote: > NONCONFIDENTIAL // EXTERNAL > So, basically, Django will not be supporting Composite Primary Keys in > the future? > > Lance > > -----Original Message----- > From: django-users@googlegroups.com <django-users@googlegroups.com> On > Behalf Of Michal Petrucha > Sent: Monday, February 11, 2019 8:34 AM > To: Django users <django-users@googlegroups.com> > Subject: [External] Re: Composite Primary / Foreign Key support > > NONCONFIDENTIAL // EXTERNAL > > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA512 > > On Mon, Feb 11, 2019 at 01:08:41AM -0800, 'Lance Ellinghaus' via Django > users wrote: > > I have seen references to people adding the support of composite > > primary keys to Django for years, but it does not look like it has been > > added. > > > > I have a number of legacy databases that I cannot add fields to but > > need to be able to be queried through Django. They are read-only tables. > > A number of the tables are also related through Composite Foreign Keys > > and I have seen some addons but not sure what is fully supported. > > > > I am trying to use Django 2.1.5. > > > > Any help or ideas would be appreciated, and saying "Add a field to > > your tables" is not an option. > > > > Thank you. > > Hi Lance, > > I haven't been on top of this in recent years, but let me try. > > When it comes to just composite primary keys, as long as you only need > read access, you might be able to get away with marking an arbitrary > field as the primary key. Using a non-unique field as the primary key > would make any writes to the database dangerous, but that's not your > case here. However, you also lose the invariant that filtering on the > “pk” field alias will match at most one row, which means the admin > would probably be off the table, too – since that assumes the “pk” is, > in fact, unique, and the same holds for any other package that makes > use of “pk”. You should still be okay in your own code, though. > > For composite foreign keys, there is nowadays a private, undocumented > API, ForeignObject, which is what ForeignKey builds on. The general > ForeignObject lets you specify multiple fields that make up the > relation, you should be able to find some examples in the test suite > (there is a foreign_object package in there). Keep in mind that this is > an internal API, so it might change without warning. > > Good luck, > > Michal > -----BEGIN PGP SIGNATURE----- > Version: GnuPG v1 > > iQIcBAEBCgAGBQJcYXniAAoJEHA7T/IPM/kl8EAP/Rzaxqe0bDO6vkxb4/Mmmj5S > 62t6Cfm3VqqK6NxYjRXG904jKwDI4HMH1SAs5fdVMh9vf+VBj/S5bcIpQbesqXbh > wbkcIn+mmnfhLDaHOGunYqp76tscBJv/rtxJZaX5NRLp7OraCWtbjRBtiw1fJ/tl > iJD0HRIk9zn0pqyX8GjeAyM0UR+uL1wwrvz8Ur85ASsc8pFThTP6ZMQoaEIgo9D+ > HB3XfrhiOMd5Nb2SbjG4KCRe7alpFx83nuY53YVsv+8X+Nqp4Ndi7ch2Ni3jxxHf > R7qVJYsMp/l72CNb6KiT85sb6PwQyeVdvU78cXKjkIKDirskGgQIEW2OvK+ZXC3B > Aj4I+AMFXEKje8ITfW3/s/v+UNvVTNZHYC5NPZ6o50+YJFDoiwb0mpQMdUredWZk > nT2cYMgyPQA/XKN9w5vUCNbTebPG/AA7yCthXbOrHn9Xl+kICkXRjjl9fHRUs55Q > wgPqz0CFXPKaE+JFt/NABJzdSrki1y587GHsOb7hKFiQwS8DHU8WOMXkR3BGKEtN > q0gebcqKvVnjRwLLsBvB0h3uI/yifgBTp8G8/+tZ0WuNdongTe+yPzchxuRjgx10 > e70xtBjgsyCQGRB3CPsgR2UelQOtAEt8ZyYwyPF5sQYOvQg1xjcYp87FqfqflSTE > 6aQIMkXhKjKazmc/ew9F > =Ji5Z > -----END PGP SIGNATURE----- > > -- > 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 django-users+unsubscr...@googlegroups.com. > To post to this group, send email to django-users@googlegroups.com. > Visit this group at https://groups.google.com/group/django-users. > To view this discussion on the web visit > https://groups.google.com/d/msgid/django-users/20190211133426.GV10973%40koniiiik.org. > 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 django-users+unsubscr...@googlegroups.com. > To post to this group, send email to django-users@googlegroups.com. > Visit this group at https://groups.google.com/group/django-users. > To view this discussion on the web visit > https://groups.google.com/d/msgid/django-users/5c6a6c98.1c69fb81.eb4fb.5c2cSMTPIN_ADDED_MISSING%40gmr-mx.google.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. 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