Wagtail API v2 django.template.exceptions.TemplateDoesNotExist

Question

I have configured Wagtail API as prescribed in the docs and it works nicely when using curl:

$ curl -LsD- http://127.0.0.1:8080/rest/p/
HTTP/1.1 200 OK
Date: Fri, 22 May 2020 17:33:58 GMT
Server: WSGIServer/0.2 CPython/3.8.2
Content-Type: application/json
Vary: Accept, Cookie
Allow: GET, HEAD, OPTIONS
X-Frame-Options: DENY
Content-Length: 433
X-Content-Type-Options: nosniff

{
    "meta": {
        "total_count": 1
    },
    "items": [
        {
            "id": 2,
            "meta": {
                "type": "wagtailcore.Page",
                "detail_url": "http://localhost/rest/p/2/",
                "html_url": "http://localhost/",
                "slug": "home",
                "first_published_at": null
            },
            "title": "Welcome to your new Wagtail site!"
        }
    ]
}

Wagtail doc state the following:

Optionally, you may also want to add rest_framework to INSTALLED_APPS. This would make the API browsable when viewed from a web browser but is not required for basic JSON-formatted output.

This is kind of true, because API works fine via curl, however if I do not add rest_framework to the INSTALLED_APPS and then try to access the same url via browser I do get http 500, namely because application throws an exception:

Internal Server Error: /rest/p/
Traceback (most recent call last):
  File "/usr/local/lib/python3.8/site-packages/django/core/handlers/exception.py", line 34, in inner
    response = get_response(request)
  File "/usr/local/lib/python3.8/site-packages/django/core/handlers/base.py", line 145, in _get_response
    response = self.process_exception_by_middleware(e, request)
  File "/usr/local/lib/python3.8/site-packages/django/core/handlers/base.py", line 143, in _get_response
    response = response.render()
  File "/usr/local/lib/python3.8/site-packages/django/template/response.py", line 105, in render
    self.content = self.rendered_content
  File "/usr/local/lib/python3.8/site-packages/rest_framework/response.py", line 70, in rendered_content
    ret = renderer.render(self.data, accepted_media_type, context)
  File "/usr/local/lib/python3.8/site-packages/rest_framework/renderers.py", line 723, in render
    template = loader.get_template(self.template)
  File "/usr/local/lib/python3.8/site-packages/django/template/loader.py", line 19, in get_template
    raise TemplateDoesNotExist(template_name, chain=chain)
django.template.exceptions.TemplateDoesNotExist: rest_framework/api.html

So it seems to me that if I don't want to jam my email with django exceptions, then rest_framework is a mandatory app in my prod site settings? Did I miss some configuration detail? What is the best way to address this issue?

I don't want that my live site would be throwing 500 all the time and also I don't strictly need this nice and shining api interface.

---

EDIT:

Added relevant rest_framework config:

REST_FRAMEWORK = {
    "DEFAULT_PERMISSION_CLASSES": [
        "rest_framework.permissions.IsAuthenticatedOrReadOnly",
    ],
    "DEFAULT_RENDERER_CLASSES": [
        "rest_framework.renderers.JSONRenderer",
    ],
}

---

EDIT:

By looking to the debug tracebacks it seems that Wagtail is somehow enforcing rest_framework.renderers.BrowsableAPIRenderer renderer, even though REST_FRAMEWORK is not configured to use it?

EDIT:

Apparently Wagtail indeed ignores REST_FRAMEWORK settings and instead uses hardcoded renderer_classes which are [JSONRenderer, BrowsableAPIRenderer].

Answer 1

Potentially it's a bug in a Wagtail as it ignores REST_FRAMEWORK configuration in the settings and instead uses hardcoded renderer_classes which currently are [JSONRenderer, BrowsableAPIRenderer].

To overcome this issue one may set up Wagtail API like the following:

from django.conf import settings
from wagtail.api.v2.views import PagesAPIViewSet
from wagtail.api.v2.router import WagtailAPIRouter

if not settings.DEBUG:
    from rest_framework.renderers import JSONRenderer

    class ProdPagesAPIViewSet(PagesAPIViewSet):
        renderer_classes = [JSONRenderer]

    PagesAPIViewSet = ProdPagesAPIViewSet

api_router = WagtailAPIRouter("wagtailapi")  
api_router.register_endpoint("p", PagesAPIViewSet)

Answer 2

This is because rest_framework has the TemplateHTMLRenderer as one of the default renderers.

REST_FRAMEWORK = {
    'DEFAULT_RENDERER_CLASSES': [
       'rest_framework.renderers.JSONRenderer',
       'rest_framework.renderers.TemplateHTMLRenderer',
    ],
   ...
}

And for it to render the templates, it has to locate them using the Django template util. And for that tool to search for the template in the rest_framework package, it has to be added to INSTALED_APPS.

So, to resolve the issue, override the REST_FRAMEWORK setting and remove the the TemplateHTMLRenderer as you only need the JSONRenderer. You can read more about DRF settings.