DRF doesn't change the media type of request body to multipart/form-data automatically

[knivets]

Checklist

• [x] I have verified that that issue exists against the master branch of Django REST framework.
• [x] I have searched for similar issues in both open and closed tickets and cannot find a duplicate.
• [x] This is not a usage question. (Those should be directed to the discussion group instead.)
• [x] This cannot be dealt with as a third party library. (We prefer new functionality to be in the form of third party libraries where possible.)
• [x] I have reduced the issue to the simplest possible case.
• [ ] I have included a failing test as a pull request. (If you are unable to do so we can still accept the issue.)

Steps to reproduce

# view.py
from rest_framework import generics
from rest_framework import serializers
from django.db import models

class Book(models.Model):
  title = models.CharField(max_length=200)

class BookSerializer(serializers.ModelSerializer):
  cover = serializers.FileField()
  class Meta:
    model = Book
    fields = ('cover',)

class BooksView(generics.CreateAPIView):
  queryset = Book.objects.all()   
  serializer_class = BookSerializer

# urls.py
urlpatterns = [
...
path('api/books/', views.BooksView.as_view()),
...
]

Expected behavior

./manage.py generateschema 
openapi: 3.0.2
info:
  title: ''
  version: TODO
paths:
  /api/books/:
    post:
      operationId: CreateBook
      parameters: []
      requestBody:
        content:
          multipart/form-data:
            schema:
              required:
              - cover
              properties:
                cover:
                  type: string
                  format: binary
      responses:
        '200':
          content:
            application/json:
              schema:
                required:
                - cover
                properties:
                  cover:
                    type: string

Actual behavior

./manage.py generateschema 
openapi: 3.0.2
info:
  title: ''
  version: TODO
paths:
  /api/books/:
    post:
      operationId: CreateBook
      parameters: []
      requestBody:
        content:
          application/json:
            schema:
              required:
              - cover
              properties:
                cover:
                  type: string
      responses:
        '200':
          content:
            application/json:
              schema:
                required:
                - cover
                properties:
                  cover:
                    type: string

There are two things going on here:

1. There is no support for automatic multipart/form-data media type generation
2. The FileField generates incomplete OpenAPI schema: it doesn't include format: binary. Finally, it should only generate format: binary for requests, since you can't have a binary string field within application/json media type. We could probably add a format: uri in case use_url=True.

https://swagger.io/docs/specification/describing-request-body/multipart-requests/

On unrelated note I noticed that DRF doesn't put type: object under schema even though this spec passes validation here

[lovelydinosaur]

Yeah seems valid to me. Of course it’s less obvious what we should do if we have both FileField and composite field types (that multipart can’t support.)

[knivets]

Could you please give an example of request body with file and composite field?

[lovelydinosaur]

Eg. Anything with both FileField and DictField

[lovelydinosaur]

Or FileField and a nested serializer

[carltongibson]

@knivets you fancy taking a pop at this? As Tom says, we should be able to do the simple cases at least.

(There may come a complexity level where we say “use a subclass to specify this particular case” rather than try and solve everything, but we’re not there yet...)

[knivets]

Yes! I’ll work on this over the weekend.

[gnuletik]

@knivets Do you have an idea what is the expected schema using OpenAPI Components ? Component's goal is to keep the same properties for request and response and reference them.

In the example you posted in "Expected behavior", the format: binary property is only in the "requestBody". Should the schema include a different component for request and response?

I wasn't able to find any example about this on the web. Thanks!