Django and REST API to serve calculation-based requests

Question

I wrote a machine learning application in Django so a user can specify in a form some parameters and train a model. Once the model is trained, I want to serve requests like:

curl http://localhost:8000/.../?model_input='XYZ' 

and I want Django returns the output of the model given the input XYZ. Every example I saw from Tastypie or REST framework builds its response from a queryset. How can I proceed if the response is not the result of a queryset but the result of in-memory pure calculation? In my case, the response is the result of a matrix multiplication (the trained model) by a vector (the input) and this result is not stored in a table.

What is the recommended way to manage such requests? Any help is greatly appreciated. Regards, Patrick

Answer 1

Django REST Framework does not require a model source, or a queryset, though it does perform its best when working with either of them. It does provide a basic Serializer for this reason, as well as basic APIView classes to allow for content negotiation to be used on top of standard Django class-based views.

You most likely won't need to use the Serializer unless you were looking to serialize the results object. The other common use for a Serializer is to validate the incoming data and convert it to an expected format.

If you were just looking to return a basic value (you didn't specify what "the result of a matrix multiplication" actually could be), then even just using the basic views is a step up from doing it all manually. The Response object that Django REST Framework provides allows you to return arbitrary data and have it be converted into a comparable JSON or XML representation, automatically. You never need to call json.dumps or coerce the data into a specific representation, the Response object does it all for you.

from rest_framework.response import Response
from rest_framework import serializers, views

class IncredibleInputSerializer(serializers.Serializer):
    model_input = serializers.CharField()

class IncredibleView(views.APIView):

    def get(self, request):
        # Validate the incoming input (provided through query parameters)
        serializer = IncredibleInputSerializer(data=request.query_params)
        serializer.is_valid(raise_exception=True)

        # Get the model input
        data = serializer.validated_data
        model_input = data["model_input"]

        # Perform the complex calculations
        complex_result = model_input + "xyz"

        # Return it in your custom format
        return Response({
            "complex_result": complex_result,
        })

In the example above, we create a IncredibleInputSerializer that validates the model_input query parameter to make sure that it is included in the request. This is a very basic example, as Django REST Framework supports doing additional things to the input, like converting it to a number or validating that it conforms to a specific format.

Of course, if you need to serialize an object or list of objects, that's where Django REST Framework excels. It doesn't have to be a model object, it can be an object with attribute or methods to get the data, or even just a basic dictionary, and Django REST Framework should be able to serialize it for you.