Fix backward Relay pagination

[tcleonard]

New version of the pull request #1010 (to solve issue #1009) which adds unit tests.

[tcleonard]

Not sure what is causing those test failures... it fails in an import in django rest framework (and the import is totally valid).
Tests are passing locally.

[zbyte64]

This is the relevant part I see from the test failure:

 .tox/py37-django111/lib/python3.7/site-packages/rest_framework/fields.py:15: in <module>
      from django.core.validators import (
  E   ImportError: cannot import name 'ProhibitNullCharactersValidator' from 'django.core.validators' (/home/runner/work/graphene-django/graphene-django/.tox/py37-django111/lib/python3.7/site-packages/django/core/validators.py)

DRF wants to import a validator from Django that doesn't exist in Django 1.11

[tcleonard]

Indeed, which is not related to anything I have changed... Maybe DRF simply decided to drop support for older versions of Django and we might need to do the same here.

[jkimbo]

@tcleonard yep DRF dropped support for Django 1.11. Fixed the tests here: #1047

[tcleonard]

thanks @jkimbo, merged your changes and the CI now passes

[zbyte64]

Thank you for this

[vecchp]

@zbyte64 is there anything that needs to be done to get this in?

[tcleonard]

I don't think so... for me it's ready to merge.. 🤷

[pcraciunoiu]

Makes sense to me. Just one change I'd suggest.

[pcraciunoiu]

In this case, max limit is lower than the number of objects, right?

It looks like this test covers the same case as this one, which is great!

[pcraciunoiu]

@jkimbo any chance we could get this merged?

Because graphene-django doesn't support true cursor pagination, the most reliable way to get recent items first is to go backwards, and this bug gets in the way of that.

[jkimbo]

Thanks @zbyte64

[tcleonard]

Thanks @zbyte64