How to response different data that was inserted by create method (ModelViewSet)

I finally managed to sort this out, and in a much more elegant way than I had been trying beforehand.

What I need to do is: add new stock instances, for this I had created a new route for POST in the endpoint resources/id.

So I was able to reuse the Default Router, delete the custom_create method, and just modified the serializers.py file. It looks like this:

serializers.py

class StockSerializer(serializers.ModelSerializer):

    class Meta:
        model = Stock
        fields = ['size', 'amount']

class ShoeSerializer(serializers.ModelSerializer):

    stock = StockSerializer(many=True)

    def update(self, instance, validated_data):
        instance.description   = validated_data.get(
            'description', instance.description)
        instance.provider  = validated_data.get(
            'provider', instance.provider)
        instance.type        = validated_data.get('type', instance.type)
        instance.cost_price = validated_data.get(
            'cost_price', instance.cost_price)
        instance.salve_price = validated_data.get(
            'sale_price', instance.sale_price)

        stock      = instance.stock.all()
        stock_data = validated_data.get('stock', [])

        for item_data in stock_data:
            item_id = item_data.get('size', None)
            if item_id is not None:
                item_db            = stock.get(size=item_id)
                item_db.size    = item_data.get('size', item_db.size)
                item_db.amount = item_data.get('amount',item_db.amount)
                item_db.save()
            else:
                Estoque.objects.create(
                    shoe = instance,
                    size    = item_data['size'],
                    amount = item_data['amount']
                )
        instance.save()
        return instance

    class Meta:
        model = Shoe
        fields = ['_id','description', 'provider', 'type', 'cost_price','sale_price','total_amount', 'stock']

Now, via PATCH verb I can add new Stock instances and alter existing stock instances. Thank you for the support!

If I understood correctly by looking at your code, in this case specifically, you don't need the StockPostSerializer. You can acheive the result you want by changing StockSerializer as follows:

class StockSerializer(serializers.ModelSerializer):

    class Meta:
        model = Stock
        fields = ['shoe', 'size', 'amount']
        extra_kwargs = {'shoe': {'write_only': True}}

I greatly apologize if I misunderstood your question.

EDIT:

Forgot to say. Using this serializer you don't need any extra route on your ModelViewSet