No, it is not the case that null=True is disallowed for FKs, but it probably should be.
In a full database setup, the existence of foreign key constraints usually means that records have to be carefully loaded in an appropriate order, otherwise the FK field in one record has no match in the table that is supposed to supply the FK. The concept of Deferrable/Initially deferred, means that the constraint does not have to be satisfied when the record is loaded, but at some future time. Not all databases have the Deferrable option, and not all have an ability to turn off constraints, but few will work properly with null values in foreign keys. It is still a very bad idea to try to force a null into a foreign key field where even the DB software will be expecting a value it can look up (expect broken queries and table joins and views), but it is not prohibited by Django. On the other hand, it can generate an error message, possibly depending on the DB employed. PostgreSQL allows Deferrable, and may accept a temporary null value. SQL Server seems to require a turning-off of relationships or constraint enforcement to load data where the FKs may not match the records in another table. And for now a good workaround is to make the one default record which is used to point to all the unknowns (edit as they become known) > > Hello, > > On Jan 23, 2008 11:17 PM, Wyley <[EMAIL PROTECTED]> wrote: >> >> Michael, >> >> Thanks for your reply! >> >> > Many databases will allow a constraint with a foreign key to be >> deferrable >> > and initially deferred so that you don't have to disable the >> relationship >> > to load data. >> >> Can you say a bit more about this? I'm by no means an expert on >> databases; I'm not quite sure what "deferable" means. >> > > I too have not quite understood this, and am now curious since I have > been using both blank=True and null=True on ForeignKeys, but haven't > had an error so far. > > To me, the original problem felt like the database wasn't in sync with > the model (allowing NULL), but apparently that's not the case? > > Also, the docs[1] have a section describing field options in which it > states that it applies to all fields. It comes right before the > descriptions for ForeignKey and ManyToMany, but it is where it defined > help_text, verbose_name and other fields that, in fact, do apply to > ForeignKeys as well. So that kind of confuses me. > > Is it really the case that null=True is not allowed for ForeignKeys? > > > [1] http://www.djangoproject.com/documentation/model-api/#field-options > > > Thanks in advance, > Eduardo. > > > > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to django-users@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/django-users?hl=en -~----------~----~----~----~------~----~------~--~---
