With drf-yasg, how can I support multiple serializers in the Response?

Question

With a response from my drf just containing the data given by a single serializer, we can implement it as:

@swagger_auto_schema(
    operation_id='ID example',
    operation_description="Description example.",
    responses={status.HTTP_200_OK: Serializer4ModelA(many=True)},
)

Which works fantastic, but with some requests constructing a dictionary, where two or three of the keys correspond to different serializers, e.g.

response = {
    "a": serializer_data_for_model_a,
    "b": serializer_data_for_model_b,
    "c": serializer_data_for_model_c
}

How can we describe that in the auto schema? I've tried a few different approaches, mostly similar to the following:

@swagger_auto_schema(
    operation_id='ID example',
    operation_description="Description example.",
    responses={status.HTTP_200_OK: openapi.Response(
        description='response description',
        schema=openapi.Schema(
            type=openapi.TYPE_OBJECT,
            properties={
                'a': Serializer4ModelA(many=True),
                'b': Serializer4ModelB(many=True),
                'c': Serializer4ModelC(many=True)
            })
    )}
)

But always fails when loading the documentation, with flex saying:

"/usr/local/lib/python3.6/site-packages/flex/utils.py", line 125, in 
get_type_for_value raise ValueError("Unable to identify type of 
{0}".format(repr(value)))
ValueError: Unable to identify type of 
Serializer4ModelA(many=True):

I've read the documentation over and over again, and scoured over github for an example, but I couldn't find an example or anyone doing this. So my question is how to successfully manually define a schema for a response that contains different serializers for different keys in the returned response?

Answer 1

What I usually do is to create another serializer (just so that drf-yasg can generate the docs).

For example if I have an endpoint that returns:

{
   "results": [..list of serialized results with serializer X...]
}

I create a second serializer:

class Y(serializers.Serializer):
    results = X(many=True)

and use Y serializer in the swagger_auto_schema decorator.

Answer 2

I ended up being able to do it, although probably not the most elegant solution but it does work.

My drf has a custom app-label format, so all my apps are in a folder, and let's call this folder apps.

In my question, for a serializer, we can replace Serializer4ModelA in the properties section of the openapi.Schema with a custom function, lets say get_serializer(Serializer4ModelA()).

So my idea was to basically construct the schema myself by getting the information automatically and automatically constructing the properties dictionary. It's very hacky, but useful for me because in my documentation I also want to pass in the serializers for Dynamodb, so I made a very similar function for Dynamodb serializers.

I only just made it, and it works, but obviously needs more attention to cover all fields in the field mapping, better dealing with SerializerMethodFields.

But none the less, it is a solution that works but is not generic, tweaks and stuff will have to be made depending on your particular project.

I implemented the function roughly as follows:

from drf_yasg import openapi
from drf_yasg.inspectors import SwaggerAutoSchema
from drf_yasg.utils import swagger_auto_schema
from drf_yasg.inspectors import FieldInspector
from drf_yasg.utils import swagger_serializer_method
import rest_framework

rest_framework_openapi_field_mapping = {
     "ListField": openapi.TYPE_ARRAY,
     "CharField": openapi.TYPE_STRING,
     "BooleanField": openapi.TYPE_BOOLEAN,
     "FloatField": openapi.TYPE_NUMBER,
     "DateTimeField": openapi.TYPE_STRING,
     "IntegerField": openapi.TYPE_INTEGER,
     "SerializerMethodField": openapi.TYPE_STRING
}

def parse_rest_framework_field(field):
    rest_framework_field_type = field.split("(")[0]
    openapi_field_type = 
    rest_framework_openapi_field_mapping[rest_framework_field_type]
    if "help_text=" in field:
        field_description = field.split("help_text='")[-1].split("'")[0]
    else:
        field_description = None
    return openapi.Schema(type=openapi_field_type, description=field_description)

def parse_serializer(serializer):
    properties = {}
    for k,v in serializer.get_fields().items():
        if v.__module__ == "rest_framework.fields":
            properties[k] = parse_rest_framework_field(str(v))
        elif v.__module__.startswith("apps."):
            serializer = str(v).strip().split("(")[0]
            exec(f"from {v.__module__} import {serializer}")
            eval_serializer = eval(f"{serializer}()")
            properties[k] = openapi.Schema(type=openapi.TYPE_OBJECT, properties=parse_serializer(eval_serializer))
        else:
            pass
    return properties

def get_serializer(serializer, description):
    """ Needs to return openapi.Schema() """
    properties = parse_serializer(serializer)
    return_openapi_schema = openapi.Schema( type=openapi.TYPE_OBJECT, properties=properties, description=description)
    return return_openapi_schema