DRF - Serializer Multiple Models - json

Question

How can I POST this JSON
{
"campaign": 27,
"campaignName": "Prueba promo",
"promotionType": 999,
"items": [
{ "item_nbr": 1234567890123, "plu": 2},
{ "item_nbr": 12345678901, "plu": 3}
]
}
Currently, I only get this response JSON
{
"items": [],
"campaign": 27,
"campaignName": "Prueba promo",
"promotionType": 999,
"start_date": "2019-03-04T12:02:16.574874-03:00",
"end_date": null,
"active": true
}
How can I do it? I read the DRF documentation but it didn't work, what I'm doing wrong?
here is my code
my models.py
class Item(models.Model):
promocion = models.ForeignKey(Promocion, related_name='items', on_delete=models.CASCADE, null=True)
item_nbr = models.IntegerField(primary_key=True, help_text="Numero de Item")
modular = models.ForeignKey(Modular, on_delete=models.CASCADE, null=True)
price = models.FloatField()
q_min = models.PositiveIntegerField(default=1, help_text="Cantidad mínima")
q_mul = models.PositiveIntegerField(default=1, help_text="Multiplo de cajas cerradas")
vensil1 = models.CharField(max_length=30, help_text="Atributo item relevante")
vensil2 = models.CharField(max_length=30, help_text="Atributo item relevante")
vensil3 = models.CharField(max_length=30, help_text="Atributo item relevante")
FG = "Fleje grande, 1/3 Carta"
FP = "Fleje pequeño 1/6 Carta"
CP = "Carteleria media Carta"
opciones = ((FG, "Fleje grande, 1/3 Carta"),
(FP, "Fleje pequeño 1/6 Carta"),
(CP, "Carteleria media Carta"),)
print_type = models.CharField(choices=opciones, help_text="Fleje a imprimir", max_length=255)
depto = models.IntegerField(default=1, help_text="Departamento")
descri = models.CharField(max_length=100, help_text="Descripción producto")
brand = models.ForeignKey(Brand, on_delete=models.CASCADE, null=True)
vendor_pack = models.IntegerField(default=1)
container = models.CharField(max_length=6, default="MAY")
size = models.CharField(max_length=20, help_text="Tamaño pack")
cont_net = models.FloatField(default=1, help_text="Contenido Neto")
sell_unit = models.CharField(max_length=5, help_text="Unidad de venta")
weight_drain = models.FloatField(default=0, help_text="Peso drenado")
cod_bal = models.IntegerField(null=True, blank=True, help_text="Código balanza")
plu = models.BigIntegerField(help_text="Código de barra")
here are my serializer.py
class ItemPromoSerializer(serializers.ModelSerializer):
class Meta:
model = Item
fields = ('item_nbr', 'plu')
class PromoSerializer(serializers.ModelSerializer):
items = ItemPromoSerializer(many=True, read_only=True)
#steps = ScalePromoSerializer(many=True)
class Meta:
model = Promocion
fields = ('items', 'campaign', 'campaignName', 'promotionType',
'start_date', 'end_date', 'active')
my viewsets.py
class PromoViewSet(viewsets.ModelViewSet):
queryset = Promocion.objects.all()
serializer_class = PromoSerializer
and my routes.py
router.register(r'promo', PromoViewSet)
I've tried methods to_internal_value() and to_representation() but the result was
"non_field_errors": ["Invalid data. Expected a dictionary, but got list."]

Answer 1

If this issue happens during a POST request, it means that you need to adapt the way you save your data. Django REST Framework doesn't support writing nested objects in DB out of the box.
What I usually do for these use cases is
I don't use viewset for such complex use cases, instead I prefer using CreateAPIView which enables me to use specific serializers to validate inputs and to present data.
I hook in create of CreateAPIView and use with transaction.atomic(): when writing to several tables at the same time to make sure all transactions are invalidated in case an error comes up.
I use 2 serializers one for the parent model and one for the child model.
In your case the code could like this:
serializer.py
class PromoSerializer(serializers.ModelSerializer):
class Meta:
model = Promocion
fields = ('campaign', 'campaignName', 'promotionType', 'start_date', 'end_date', 'active')
class ItemPromoSerializer(serializers.ModelSerializer):
class Meta:
model = Item
fields = ('item_nbr', 'plu')
viewsets.py
from rest_framework import status
from django.db import transaction
class PromoCreateAPI(CreateAPIView):
queryset = Promocion.objects.all()
serializer_class = PromoSerializer
# We skip perform_create
def create(self, request, *args, ***kwargs):
try:
items_data = request.data.pop('items')
except KeyError:
return Response({}, status=status.HTTP_400_BAD_REQUEST)
serializer = self.get_serializer(data=request.data)
serializer.is_valid(raise_exception=True)
with transaction.atomic():
instance = serializer.save()
# Validate each item
for item in items_data:
s = ItemPromoSerializer(data=item)
s.is_valid(raise_exception=True)
s.save(campaign=instance)
headers = self.get_success_headers(serializer.data)
serializer.data['items'] = items_data
return Response(serializer.data, status=status.HTTP_201_CREATED, headers=headers)
Of course this code is untested, but I hope it helps you get where you need to.