Django REST Framework : serializer fields are missing in the response - django

Question

I'm using Django 2.0 and Django REST Framework.
I have two models contact and transaction as below
contact model
class Contact(models.Model):
user = models.ForeignKey(User, on_delete=models.CASCADE)
first_name = models.CharField(max_length=100)
last_name = models.CharField(max_length=100, blank=True, null=True)
amount given model
class AmountGiven(models.Model):
contact = models.ForeignKey(Contact, on_delete=models.PROTECT)
amount = models.FloatField(help_text='Amount given to the contact')
interest_rate = models.FloatField(blank=True, default=None, null=True, help_text='% of interest to be calculated')
_given_date = models.DateTimeField(
db_column='given_date',
default=timezone.now,
help_text='Date and time when amount was given to the contact'
)
def __str__(self):
return str(self.amount)
#property
def given_date(self):
return self._given_date
#given_date.setter
def given_date(self, value):
self._given_date = value
#property
def interest_to_pay(self):
if self.interest_rate:
datetime_diff = datetime.now(get_localzone()) - self.given_date
days = datetime_diff.days
duration_in_year = days/365
simple_interest_amount = (self.amount * duration_in_year * self.interest_rate)/100
return simple_interest_amount
return 0
#property
def total_payable(self):
return self.amount + self.interest_to_pay
#property
def amount_due(self):
returned_amount = 0
for returned in self.amountreturned_set.all():
returned_amount += returned.amount
return self.total_payable - returned_amount
and ContactSerializer
class ContactSerializer(serializers.HyperlinkedModelSerializer):
url = serializers.HyperlinkedRelatedField(
view_name='contacts:detail',
read_only=True
)
user = serializers.CurrentUserDefault()
amount_due = ReadOnlyField(source='amountgiven__amount_due')
class Meta:
model = Contact
fields = ('url', 'id', 'first_name', 'last_name', 'full_name', 'amount_due')
and in views.py
class ContactViewSet(viewsets.ModelViewSet):
serializer_class = ContactSerializer
permission_classes = (IsAuthenticated, AdminAuthenticationPermission,)
def get_queryset(self):
return Contact.objects.filter(user=self.request.user)
def perform_create(self, serializer):
serializer.save(user=self.request.user)
But there is no field as amount_due and url in the response returned while making the request to /contacts/ endpoint with GET method.

Answer 1

Based on your comment, you want the sum of all the amounts(please edit your question). so you should use annotate in your queryset:
from django.db.models import Sum
def get_queryset(self):
return Contact.objects.filter(user=self.request.user).annotate(amount_due=Sum('amountgiven_set__amount'))
(I recommend using modelManager for the queryset and the filtering instead of doing it here)
and add a field like this to your serializer:
amount_due = serializer.IntegerFiled()

Answer 2

Your modeling doesn't allow you to access amount_due in the way which you'd like.
Your Contact model does not have amountgiven attribute.
It does however have amountgiven_set which you can use to obtain a queryset of amountgiven for given contact.
But there can be multiple ones so you need to decide which amount_due you want to display in your serializer.
You can use SerializerMethodField to serializer the value of amount_due which you would like:
class ContactSerializer(serializers.HyperlinkedModelSerializer):
amount_due = serializers.SerializerMethodField()
def get_amount_due(self, obj):
amountgiven = obj.amountgiven_set.first()
return amountgiven.amount_due
But again, as i already mentioned - amountgiven_set returns a queryset where you can have multiple objects.
In case you are sure you have only one for given contact, you can use first() as in my example to get it.