Filter method and lookup expressions

[Subaku]

Hi,

Seems like a potential bug. Declaring a method on a field in my FilterSet seems to not do anything under a couple of scenarios.

1. If the field is a DateTimeField my method is not called
2. If I add any lookup expression to my query it seems to not get called.

Am I just expecting too much of the method?

For reference I had the filter working before without a declared method by defining the following in my Meta:

class Meta:
   model = MyModel
   fields = {
      when_seen: ['gt', 'gte', 'lt', 'lte'],
      ...
   }

Which worked great. I now need a method so I can customize what happens if the user filters by __gt or __gte. So I figured I could simple remove the when_seen from my meta and declare:

when_seen = rest_filters.DateTimeFilter(field_name='when_seen', method='by_when_seen')

Yet no matter what I do my method does not get called. Any ideas?

[rpkilby]

Hi @Subaku. This isn't actually related to the method argument, but the more general case that you declared filters cannot be used as a base for generating filters for additional lookups. In general, the following is invalid:

class F(FilterSet):
    name = CharFilter(field_name='username')

    class Meta:
        model = User
        fields = {'name': ['exact', 'gt', 'lt']}

However, there is a bug and filter generation doesn't warn you that the additional filters aren't generated. This has been fixed in #1061, but the change hasn't been released yet. That said, the fix is just raising a warning instead of silently failing. This kind of filter generation won't work, and you'll have to declare these filters manually.

Additionally, you might be interested in #1150. One deficiency with the current filter method implementation is that you don't get additional arguments like lookup_expr. By passing the filter instance to the filter method, you can then access any argument, including the lookup. The PR also describes current workarounds.

[Subaku]

Thanks for pointing out #1150. I'll try that workaround.

Also sorry for not being clearer in my post. I'm aware you can't do what you show. I'm not trying to declare both a manual filter field AND the same field in the Meta. I'm doing either or. That said my proposed, possible bug still stands. I.e.

class F(FilterSet):
    dt = DateTimeFilter(field_name='when_seen', method='get_dt_now')

    class Meta:
        model = User

    def get_dt_now(...):
         ...

For whatever reason get_dt_now never gets called... But if I instead change it to a CharField it works.

Thanks again.

[rpkilby]

I'm aware you can't do what you show. I'm not trying to declare both a manual filter field AND the same field in the Meta. I'm doing either or.

Right, it's not the declared filter that's an issue, it's generating the filters for the other lookups. In the example I posted above, it's the name__lt, name__gt filters that wouldn't be created.

For whatever reason get_dt_now never gets called... But if I instead change it to a CharField it works.

You most likely have a validation error. Here's an example test case that I used to validate that DateTimeFilter is compatible with Filter.method.

    def test_datetime_filter(self):
        class F(FilterSet):
            dt = DateTimeFilter(field_name='published', method='get_dt_now')

            class Meta:
                model = Article
                fields = ['dt']

            def get_dt_now(self, qs, name, value):
                raise Exception('!!')

        f = F({'dt': '2020-01-01 00:00:00'})
        self.assertTrue(f.is_valid())
        with self.assertRaisesMessage(Exception, ('!!')):
            f.qs

If you check your filter's errors attribute, I'd bet that you'll see a validation error there.

[Subaku]

Yup! It was a validation error. Thanks for your response :)
I got it working using the example in #1150.