If I need to change some field values before saving to the database as I think models method clear() is suitable. But I can't call him despite all my efforts.

For example fields email I need set to lowercase and fields nda I need set as null

models.py

class Vendors(models.Model):nda = models.DateField(blank=True, null=True)parent = models.OneToOneField('Vendors', models.DO_NOTHING, blank=True, null=True)def clean(self):if self.nda == "":self.nda = Noneclass VendorContacts(models.Model):....vendor = models.ForeignKey('Vendors', related_name='contacts', on_delete=models.CASCADE)email = models.CharField(max_length=80, blank=True, null=True, unique=True)def clean(self):if self.email:self.email = self.email.lower()

serializer.py

class VendorContactSerializer(serializers.ModelSerializer):class Meta:model = VendorContactsfields = (...'email',)class VendorsSerializer(serializers.ModelSerializer):contacts = VendorContactSerializer(many=True)class Meta:model = Vendorsfields = (...'nda','contacts',)def create(self, validated_data):contact_data = validated_data.pop('contacts')vendor = Vendors.objects.create(**validated_data)for data in contact_data:VendorContacts.objects.create(vendor=vendor, **data)return vendor

views.py

class VendorsCreateView(APIView):"""Create new vendor instances from form"""permission_classes = (permissions.AllowAny,)serializer_class = VendorsSerializerdef post(self, request, *args, **kwargs):serializer = VendorsSerializer(data=request.data)try:serializer.is_valid(raise_exception=True)serializer.save()except ValidationError:return Response({"errors": (serializer.errors,)},status=status.HTTP_400_BAD_REQUEST)else:return Response(request.data, status=status.HTTP_200_OK)

As I learned from the documentation

Django Rest Framework serializers do not call the Model.clean whenvalidating model serializers

In dealing with this problem, I found two ways to solve it. 1. using the custom method at serializer. For my case, it looks like

class VendorsSerializer(serializers.ModelSerializer):contacts = VendorContactSerializer(many=True)

class Meta:model = Vendorsfields = (...'nda','contacts',)def create(self, validated_data):contact_data = validated_data.pop('contacts')vendor = Vendors.objects.create(**validated_data)for data in contact_data:VendorContacts.objects.create(vendor=vendor, **data)return vendordef validate(self, attrs):instance = Vendors(**attrs)instance.clean()return attrs

2. Using full_clean() method. For me, it looks like

class VendorsSerializer(serializers.ModelSerializer):contacts = VendorContactSerializer(many=True)

class Meta:model = Vendorsfields = (...'nda','contacts',)def create(self, validated_data):contact_data = validated_data.pop('contacts')vendor = Vendors(**validated_data)vendor.full_clean()vendor.save()for data in contact_data:VendorContacts.objects.create(vendor=vendor, **data)return vendor

But in both cases, the clean() method is not called. I really don't understand what I'm doing wrong.

For DRF you can change your serializer before save as below...

First of all, you should check that serializer is valid or not, and if it is valid then change the required object of the serializer and then save that serializer.

if serializer.is_valid():serializer.object.user_id = 15  # For example serializer.save() 

UPD! views.py

class VendorsCreateView(APIView):"""Create new vendor instances from form"""permission_classes = (permissions.AllowAny,)serializer_class = VendorsSerializerdef post(self, request, *args, **kwargs):data = request.dataif data['nda'] == '':data['nda'] = Nonefor contact in data['contacts']:if contact['email']:print(contact['email'])contact['email'] = contact['email'].lower()serializer = VendorsSerializer(data=request.data)try:serializer.is_valid(raise_exception=True)serializer.save()except ValidationError:return Response({"errors": (serializer.errors,)},status=status.HTTP_400_BAD_REQUEST)