Django-rest-framework: Allow mocking of Request objects

[mlissner]

I posted about this on the mailing list and in IRC. I've been trying to serialize a model that has a few HyperLinkRelated fields, and I get the impression it's very hard.

The drf documentation on serializers has a section that says you can simply do:

from rest_framework.renderers import JSONRenderer
serializer = CommentSerializer(comment)
json = JSONRenderer().render(serializer.data) 

Unfortunately, this doesn't work for HyperLinked relationships. When you try to do it with them, you get something like:

AssertionError: HyperlinkedIdentityField requires the request in the serializer context. Add context={'request': request} when instantiating the serializer.

So, I figured out I can add context attribute, like:

r = Request(request=HttpRequest())
context = dict(request=r)
serializer = CommentSerializer(comment, context=context)
json = JSONRenderer().render(serializer.data)

Which then returns the error:

django.core.exceptions.ImproperlyConfigured: Could not resolve URL for hyperlinked relationship using view name "opinioncluster-detail". You may have failed to include the related model in your API, or incorrectly configured the lookup_field attribute on this field.

On IRC, somebody suggests a crazy fix involving patching the reverse method of the serializer:

in the __init__ of my serializer, I called super() then looped through the Hyperlinked fields and set fieldobj.reverse = patched_reverse where patched_reverse wraps rest_framework.reverse but sets "urls" module as the urlconf kwarg

I could do that, but I'd love if there was a better solution. I think this bug request is basically:

• Is there a way to make this work?
• If so, can we document it?
• If not, can we implement such a way?

Thanks,

Mike

[mlissner]

I finally figured this out. For some reason you must manually set the version and the versioning_scheme:

r = RequestFactory().request()
r.version = 'v3'
r.versioning_scheme = URLPathVersioning()
context = dict(request=r)
renderer = JSONRenderer()
json_str = renderer.render(
    serializer(item, context=context).data,
    accepted_media_type='application/json; indent=2',
)

This seems to work, but the HyperLinkRelated values in the JSON that is serialized have the server set to testserver. I could get around that by setting:

r.META['SERVER_NAME']

But I also need to set r.scheme to https, which doesn't seem to be possible (you get an error that r.scheme cannot be set).

I don't know if this is now a documentation issue or a bug. Either would be helpful for future people.

[tomchristie]

This _is_ an awkward thing to do yes. Hyperlinked relationships _plus_ versioning in the URL doesn't work terribly well if you want to mock up requests and use them outside of a normal view context.

(Eg. the versioning scheme only gets applied to a request at the point of a view)

The best way for us to resolve this would be to make it easier to mock Request objects. (That could _optionally_ include a view argument so that the versioning scheme / accepted media type can be determined on the request object)

[tomchristie]

I've retitled this issue accordingly.

[mlissner]

That sounds like a good strategy. What made sense to me at one point was also to use the path attribute on the request to get the version, just like, I presume, a normal web request would.

[tomchristie]

What made sense to me at one point was also to use the path attribute on the request to get the version, just like, I presume, a normal web request would.

Indeed yes - the mocked request would need to include an appropriate path if path based versioning is being used, in order for serializers to correctly reverse the resulting URLs.

[tomchristie]

And apologies for your pain on this - you hit an awkward corner there! :-/

[PetrDlouhy]

Some notes to other desperate sweepers of awkward corners:

• The versioning_scheme did not work for me, but it might help, if you add version namespace into definition of the field, like serializers.HyperlinkedIdentityField(view_name="v1:downloads-detail")
• If you want to specify the host, you can do by HTTP_HOST parameter to the request()
• For me works a bit simpler request mocking code:

        from django.test import RequestFactory

        request = RequestFactory().request(HTTP_HOST='localhost:8001')
        serializer = AssetSerializer(context={'request': request})
        obj_json = serializer.to_representation(obj)

• With django.site framework, you can get the http_host like:

        from django.contrib.sites.models import Site
        http_host = Site.objects.get_current().domain

[rpkilby]

Note to self - work from #5609 might be relevant.

[stuaxo]

@rpkilby now https://github.com/encode/django-rest-framework/pull/5609 is merged does that move this along?

[stuaxo]

I'm trying to follow this to render data via a class that implements ListModelMixin and this seems even more tricky, I can't work out how to pass my queryset to the .list() method and get something out the other side.

[stuaxo]

Looking at the docs I realised i needed to call .as_view() to get realise the view and be able to call .as_list()

import sys

from display_xml import XML

from workbaskets.views import *

items_list = ItemsViewSet.as_view({'get': 'list'})
response = items_list(request, workbaskets, format='xml')

print(response.rendered_content)