Re: .filter() and .exclude() don't add up

You really should figure out which record isn't showing up in either sub case and look at it in detail to see if NULLs are involved before you spend time trying to fix a problem that you don't have.

You could, for example collect all the ids from the several queries into python sets, union the sub queries, and take the difference of that from the total query.

On Fri, Jul 26, 2013 at 5:28 PM, Daniele Procida <daniele@vurt.org> wrote:

On Fri, Jul 26, 2013, Steve McConville <mcconville.steve@gmail.com> wrote:

>Firstly (and I don't think this is the cause of the problem) you're
>calling datetime.now() four times, which will give you four different
>datetimes (ie. the queries will not be completely identical).

Good point, I will address that.

> Secondly
>SQL uses a 3-valued logic (with null) so if any of the fields you're
>filtering on are nullable you may not be able to rely on the law of
>the excluded middle

So, if one of the fields can be Null, then *neither*:

    queryset.filter(field=value)

    queryset.exclude(field=value)

will match a record where it's Null?

In that case, is there a better - more reliable - way than using both .filter() and .exclude() with the same terms to split a queryset into all those items that match a filter, and all those that don't?

Thanks,

Daniele

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