null=True tells Django to STORE a null value--this is why your unit tests
would succeed--because no attempt was made to store a null. It was a
situation where key storage was deferred.
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.
But a nullable foreign key? Not likely. Anyway, Django is trying to
store a null value into the FK, which is definitely a flaw. The value
should only be deferred. That is a flaw in your setup and also a flaw in
Django. It should not permit the setup for storing null values into a FK.
The proper way to handle that is to make one entry that is a 'default' or
'unknown' in supplier, with a genuine key, and let that be the value
stored for the FK if you are uncomfortable with a deferred FK.
Just remember that a FK implies that there is always one supplier which
may supply many items. If there are several suppliers which can supply
one item, and several items available from a single supplier, a
ManyToManyField is appropriate.
Check Table B-5 in the appendix of the Django Book. The options there for
Foreign Key do not include null=True. It is a flaw that the null=True is
not filtered from the Model, but then that is more code for no good
purpose except to produce an error message, and you already have one of
those, even if it is a bit cryptic.
Michael Moore
>
> Update: in the SQL for the Title table,
>
> CREATE TABLE "core_title" (
> ...
> "supplier_id" integer NULL,
> );
>
> Two things to note:
> 1. the SQL explicitly allows the supplier field to be NULL
> 2. the 'REFERENCES "core_contact" ("id") clause is conspicuously
> absent
>
>
> On Jan 23, 6:12 pm, Wyley <[EMAIL PROTECTED]> wrote:
>> Hello all,
>>
>> I have a model with a ForeignKey field that sets null=True:
>>
>> class Title(models.Model):
>> #...
>> supplier = models.ForeignKey(Contact, verbose_name='Supplier',
>> null=True)
>>
>> ...but when I try to save an instance without a supplier:
>>
>> >>> t = Title()
>> >>> t.save()
>>
>> [complete Traceback below...]
>> IntegrityError: core_title.supplier_id may not be NULL
>>
>> Even weirder, this error does not occur when I save Title objects
>> without a supplier in some of my unit tests -- at least, all tests
>> succeed.
>>
>> Is there some reason that Django would implicitly forbid this field to
>> be NULL, despite my having explicitly set null=True in the model?
>>
>> I am using sqlite3 and Django 0.96, if that's relevant.
>>
>> Thanks,
>> Richard
>>
>> -----------------------------------------------------------------------------------------------------------------------
>> Traceback (most recent call last):
>> File "<console>", line 1, in <module>
>> File "/var/lib/python-support/python2.5/django/db/models/base.py",
>> line 238, in save
>> ','.join(placeholders)), db_values)
>> File "/var/lib/python-support/python2.5/django/db/backends/util.py",
>> line 12, in execute
>> return self.cursor.execute(sql, params)
>> File "/var/lib/python-support/python2.5/django/db/backends/sqlite3/
>> base.py", line 93, in execute
>> return Database.Cursor.execute(self, query, params)
>> IntegrityError: core_title.supplier_id may not be NULL
> >
>
--~--~---------~--~----~------------~-------~--~----~
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
-~----------~----~----~----~------~----~------~--~---
