On Tue, Aug 11, 2009 at 10:40 AM, Alex Gaynor <alex.gay...@gmail.com> wrote:

>
> On Tue, Aug 11, 2009 at 8:25 AM, gentlestone<tibor.b...@hotmail.com>
> wrote:
> >
> > On 11. Aug, 15:01 h., Gustavo Henrique <gustavo...@gmail.com> wrote:
> >> Try also: null=True, blank=True
> >>
> >> --
> >> Gustavo Henriquehttp://www.gustavohenrique.nethttp://
> blog.gustavohenrique.net
> >
> > blank=True ... I have had, but this one doesn't solve the problem,
> > maybe the problem is in postgresql, the associated SQL code for
> > postgresql is
> >
> > CREATE TABLE ...
> > ...
> > UNIQUE ("some_fk_field_id", "some_plain_field"),
> >
> > and this apparently doesn't work
> > >
> >
>
> You are talking about in the forms/admin validation correct?  Thinking
> to how this is implemented there likely is a bug where this doesn't
> use the SQL concept of NULL != NULL and uses the Python None == None
> instead, which of these behaviors is correct I'm not sure of (though I
> lean towards the SQL interpretation).
>

I don't believe there is a bug.  The original description of the problem
confused me because I thought it was trying so specify unique_together for a
field in one model and a field in another model related by a nullable
foreign key, and I didn't think you could do that.  In fact you can't -- all
the fields have to be in the same model/table and I see now that the
original report wasn't saying that.  (The _field in the unique_together spec
is what confused me as I read that as having a double underscore.)

Anyway, form validation allows multiple allows multiple None/NULL values
here since most of the database backends interpret NULL != NULL at the SQL
level to mean that (NULL, v1) != (NULL, v1) when doing multiple field unique
checks.  The one exception I know of is Oracle, it apparently will raise an
IntegrityError for this case.  See the discussion here:

http://code.djangoproject.com/ticket/9039#comment:10

Karen

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