Django REST Framework: default fields in browseable API form - django

Question

I have a model:
class XCall(models.Model):
created_on = models.DateTimeField(auto_now_add=True)
send_on = models.DateTimeField(default=datetime.now)
recipient = models.ForeignKey(User)
text = models.CharField(max_length=4096)
backup_calls = models.IntegerField(blank=True, null=True)
And a serializer for that model:
class CallSerializer(serializers.HyperlinkedModelSerializer):
url = serializers.HyperlinkedIdentityField(
view_name='call-detail',
)
# some validation and custom field definitions
...
class Meta:
model = XCall
fields = ('url', 'id', 'text', 'recipient', 'send_on', 'backup_calls', 'status')
lookup_field= 'pk'
And here's the list view:
class CallList(generics.ListCreateAPIView):
serializer_class = CallSerializer
permission_classes = (permissions.IsAuthenticatedOrReadOnly, IsOwnerOrSuperuser,)
def pre_save(self, obj):
auth_user = self.request.user
obj.auth_user = auth_user
def get_queryset(self):
"""
This view should return a list of all the calls
for the currently authenticated user.
"""
auth = self.request.user
if isinstance(auth, AnonymousUser):
return []
elif auth.is_superuser:
return XCall.objects.all()
else:
return XCall.objects.filter(auth_user=auth)
In CallList's browseable API, I see the following in the POST form at the bottom:
My question is: why is there no default value set for send_on, and there is one for backup_calls? I assumed that the form would follow the XCall model specification and use datetime.now() for defaulting the former, and leave backup_calls blank (since it's nullable). How can I get the form to follow the model specifications?

Answer 1

You actually want to set an initial value, not a default value. See the docs. Your code should be:
from django.utils import timezone
class CallSerializer(serializers.HyperlinkedModelSerializer):
send_on = serializers.DateTimeField(initial=timezone.now())
...
A default value is the value provided to an attribute if no value is set for the field. The distinction between initial and default arguments mirrors the difference between Django's initial argument for form fields and Django's default argument for model fields.

Answer 2

There is a distinction between model defaults and initial values in forms. This is especially the case for default values which are actually functions because they are only called when the instance is saved. For example, which now do you want - this time at which the blank form is displayed, or the time at which the user presses "POST"? Django applies the default when saving the model if the field value is missing. To achieve what you want you need to manually set the default in the serialize field, for example:
class CallSerializer(serializers.HyperlinkedModelSerializer):
send_on = serializers.DateTimeField(default=datetime.now)
...