How to make calculations after requesting with M2M fields (DRF) - django

Question

class Product(models.Model):
name = models.CharField(max_length=255)
ht = models.CharField(default=0)
wd = models.CharField(default=0)
len = models.CharField(default=0)
class Parcel(models.Model):
product_list = models.ManyToManyField(Product)
class ParcelSerializer(serializers.ModelSerializer):
class Meta:
model = Parcel
fields = '__all__'
class ProductSerializer(serializers.ModelSerializer):
product_volume = serializers.ReadOnlyField()
class Meta:
model = Product
fields = '__all__'
class ParcelCreateView(generics.CreateAPIView):
queryset = Package.objects.all()
serializer_class = PackageSerializer
class ParcelListView(generics.ListAPIView):
serializer_class = ParcelSerializer
class ProductCreateView(generics.CreateAPIView):
queryset = Product.objects.all()
serializer_class = ProductSerializer
class ProductListView(generics.ListAPIView):
queryset = Product.objects.all()
serializer_class = ProductSerializer
My output is:
[
{
"id": 1,
"products": [
1
]
},
{
"id": 2,
"products": [
1,
2
]
}
]
http://127.0.0.1:8000/parcel/create
How can I get product id and product volume as below when I post parcel create? I didn't understand what to do because it's ManyToManyField. After the request comes, how can I get product ids from the body and calculate their volume
[
{
"id": 1,
"products": [
1 : Result #Volume of ID : 1 Product (wd*ht*len)
]
},
{
"id": 2,
"products": [
1 : Result #Volume of ID : 1 Product (wd*ht*len),
2 : Result #Volume of ID : 1 Product (wd*ht*len)
]
}
]

Answer 1

You can work with a serializer in your ParcelSerializer:
class ProductSerializer(serializers.ModelSerializer):
# …
pass
class ParcelSerializer(serializers.ModelSerializer):
products = ProductSerializer(many=True)
class Meta:
model = Parcel
fields = '__all__'
You thus need to define the ProductSerializer first, and then use that in the ParcelSerializer.
If you want to return the outcome of str(…) on a Product, you can work with the StringRelatedField [drf-doc]:
class ParcelSerializer(serializers.ModelSerializer):
products = StringRelatedField(many=True)
class Meta:
model = Parcel
fields = '__all__'
then this will thus produce a list of strings.