Add a "not equal" lookup for filters

[daviddavis]

fixes #5868
https://pulp.plan.io/issues/5868

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[daviddavis]

Feedback welcome here on what we want to name this. The django example used ne.

[dralley]

ne seems like an acceptable name for me

[bmbouter]

Thank you for this. I can't see a better way to do it in DRF or django-filter, so let's use this. 👍

[daviddavis]

I'm looking at a package called django-rest-framework-filters since it has support for negating filters:

https://github.com/philipn/django-rest-framework-filters#automatic-filter-negationexclusion

It basically adds some extra DRF functionality to django-filter.

[daviddavis]

I had a chance to look into django-rest-framework-filters and it seems to work pretty well (at least for searching on NOT conditions). Moreover, you can combine it with other lookups (e.g. GET /pulp/api/v3/repositories/file/file/name__contains!=RHEL).

The only downside is we have to use a prerelease version from September 2018 (1.0.0.dev0) and it looks like there is no timeline for a 1.0.0 release.

I'm torn and don't have a strong opinion on whether to just go with this PR or use drf-filters.

[bmbouter]

I also don't have a strong opinion. If it's working and that project is already dedicated to that type of feature set I lean towards using django-rest-framework-filters. @dralley do you see a downside to using django-rest-framework-filters?

I think we should go w/ the django-rest-framework-filters project.

[dralley]

I agree that we should use the 3rd party package with one caveat:

We should make sure it's compatible with the range filters we currently support on some fields

https://github.com/philipn/django-rest-framework-filters#multiwidget-is-incompatible
https://github.com/pulp/pulpcore/blob/master/pulpcore/app/viewsets/base.py#L26

(I think it is compatible, but the range bit stuck out as something to look into)

[daviddavis]

I plan to merge this on Monday February 10th. django-rest-framework-filters uses ! for NE fields which is a nonstarter for us since field names with ! won't work with the bindings.