Writable nested serializers with inherited django models - django

Question

I'm struggling to update records with the writeable nested serializers I've created.
There are many Listing categories for a classifieds app I'm creating that each have a few unique attributes, but they also share many attributes. I have a handful of django models that inherit from a parent Listing model, and one of these models, Battery, contains some nested data. So far I've been able to create Battery records but keep getting AttributeErrors when I try to update them.
I've tried to include only the relevant code. Here are my views:
# views.py
class ListingCreateView(CreateAPIView):
queryset = Listing.objects.all()
def get_serializer_class(self):
category = self.request.data['category']
if category == 1:
return PercussionSerializer
elif category == 6:
return BatterySerializer
return ListingSerializer
class ListingUpdateView(UpdateAPIView):
queryset = Listing.objects.all()
def get_serializer_class(self):
category = self.request.data['category']
if category == 1:
return PercussionSerializer
elif category == 6:
return BatterySerializer
return ListingSerializer
here are my models:
# models.py
## Parent model
class Listing(models.Model):
title = models.CharField(max_length=100)
description = models.TextField(blank=True)
price = models.DecimalField(max_digits=9, decimal_places=2, blank=True, null=True, default=0.00)
## One of the child models
class Battery(Listing):
model_name = models.TextField(blank=True, null=True, default="")
color = models.ForeignKey(Color, on_delete=models.CASCADE, blank=True, null=True)
manufacture_year = models.IntegerField(null=True)
## Model for the nested data in Battery model
class Drum(models.Model):
drum_type = models.CharField(max_length=50, blank=True)
size = models.TextField(blank=True, null=True, default="")
battery = models.ForeignKey(Battery, related_name='drums', on_delete=models.CASCADE, null=True)
and here are my serializers:
# serializers.py
class ListingSerializer(serializers.ModelSerializer):
class Meta:
model = Listing
fields = '__all__'
class DrumSerializer(serializers.ModelSerializer):
class Meta:
model = Drum
fields = ['drum_type', 'size', 'carrier', 'stand', 'cover', 'case', 'sold']
class BatterySerializer(serializers.ModelSerializer):
drums = DrumSerializer(many=True)
class Meta:
model = Battery
fields = ['id', 'title', 'description', 'price', 'model_name', 'color', 'manufacture_year', 'drums']
def create(self, validated_data):
drum_data = validated_data.pop('drums')
battery = Battery.objects.create(**validated_data)
for drum_data in drum_data:
Drum.objects.create(battery=battery, **drum_data)
return battery
def update(self, instance, validated_data):
# Update Listing field values
instance.title = validated_data.get('title', instance.title)
instance.description = validated_data.get('description', instance.description)
instance.price = validated_data.get('price', instance.price)
# Grab the Battery record for this Listing and update its values
instance_battery = Battery.objects.get(pk=instance.pk)
instance_battery.model_name = validated_data.get('model_name', instance_battery.model_name)
instance_battery.color = validated_data.get('color', instance_battery.color)
instance_battery.manufacture_year = validated_data.get('manufacture_year', instance_battery.manufacture_year)
# Check for a list of drums
drum_data = validated_data.pop('drums')
# If it exists
if drum_data:
# Clear the existing drums
instance_battery.drums.clear()
# Create new drums
Drum.objects.bulk_create(
[
Drum(**drum)
for drum in drum_data
],
)
# Save the updated Listing & Battery
instance.save()
instance_battery.save()
# Return the updated Battery
return instance
I feel like I've followed the DRF documentation about writeable nested serializers correctly, but I continue to get this AttributeError when I try to post an update to a Battery record:
AttributeError: Got AttributeError when attempting to get a value for field drums on serializer BatterySerializer.
The serializer field might be named incorrectly and not match any attribute or key on the Listing instance.
Original exception text was: 'Listing' object has no attribute 'drums'.
Judging by the error message I think the Django model inheritance requires a more specific solution that what the DRF documentation provides. Can anybody help me understand how to create the serializers I need to create/update a Battery record that inherits from a Listing model with a nested list of Drum records?
Thanks!

Answer 1

I think the problem appears because the view waits for a Listing instance. I can suggest the following: try to redefine def get_qyeryset(self)
For example:
class ListingUpdateView(UpdateAPIView):
def get_queryset(self):
if self.request.data['category'] == 6:
return Battery.objects.all()
else:
return Listing.objects.all()
def get_serializer_class(self):
category = self.request.data['category']
if category == 1:
return PercussionSerializer
elif category == 6:
return BatterySerializer
return ListingSerializer
Maybe it is not the best way, but it can solve your problem