what is the control flow of django rest framework - django

Question

I am developing an api for a webapp. I was initially using tastypie and switched to django-rest-framework (drf). Drf seems very easy to me. What I intend to do is to create nested user profile object. My models are as below
from django.db import models
from django.contrib.auth.models import User
class nestedmodel(models.Model):
info = models.CharField(null=True, blank=True, max_length=100)
class UserProfile(models.Model):
add_info = models.CharField(null=True, blank=True, max_length=100)
user = models.OneToOneField(User)
nst = models.ForeignKey(nestedmodel)
I have other models that have Foreignkey Relation. My Serializers are as below
from django.contrib.auth.models import User, Group
from rest_framework import serializers
from quickstart.models import UserProfile, nestedmodel
class NestedSerializer(serializers.HyperlinkedModelSerializer):
class Meta:
model = nestedmodel
fields = ('info', )
class UserSerializer(serializers.HyperlinkedModelSerializer):
class Meta:
model = User
fields = ('url', 'username', 'email', 'groups')
class GroupSerializer(serializers.HyperlinkedModelSerializer):
class Meta:
model = Group
fields = ('url', 'name')
class UserProfileSerializer(serializers.HyperlinkedModelSerializer):
user = UserSerializer()
nst = NestedSerializer()
class Meta:
model = UserProfile
user = UserSerializer(many=True)
nested = NestedSerializer(many=True)
fields = ('nst', 'user')
I can override methods like create(self, validated_data): without any issues. But What I want to know is to which method should the response returned by create() goes, or in other words Which method calls create(). In tastypie Resources.py is the file to override to implement custom methods. And Resources.py contains the order in which methods are being called. Which is the file in drf that serves the same purpose and illustrates the control flow like Resources.py in tastypie?.

Answer 1

So the flow goes something like:
Viewset's create() method which is implemented in CreateModelMixin
That creates serializer and validates it. Once valid, it uses viewset's perform_create()
That calls serializer's save() method
That then in turn calls serializer's either create() or update() depending if instance was passed to serializer (which it was not in step 1)
create() or update() then create/update instance which is then saved on serializer.instance
Viewset then returns response with data coming from serializer.data
serializer.data is actually a property on serializer which is responsible for serializing the instance to a dict
To serialize data, to_representation() is used.
Then response data (Python dict) is rendered to a output format via renderers which could be json, xml, etc
And Resources.py contains the order in which methods are being called. Which is the file in drf that serves the same purpose and illustrates the control flow like Resources.py in tastypie?.
Guess that would be a combination of files. Its probably better to think in terms of classes/concepts you are touching since in DRF you can inherit from multiple things for create your classes. So the thing which glues everything together are viewsets. Then there are various viewset mixins which actually glue the viewset to the serializer and different CRUD operations.

Answer 2

I figured out second part of question myself. get/create object can be done by using custom code in overriden def create(self, request, *args, **kwargs): in views.py. Code is as pasted below. Once Again, for clarity this is views.py not serializers.py. Also json with posted values can be accessed from request.DATA
class NestedViewSet(viewsets.ModelViewSet):
"""
API endpoint that allows Nested objects to be viewed or edited.
"""
queryset = nestedmodel.objects.all()
serializer_class = NestedSerializer
def create(self, request, *args, **kwargs):
info = request.DATA['info']
user = User.objects.get(username=request.DATA['user']['username'])
profile = UserProfile.objects.get(user=user)
nst = nestedmodel.objects.create(info=info, user=user, profile=profile)
serialized_obj = serializers.serialize('json', [ nst, ])
json_serialized = json.loads(serialized_obj)
data = json.dumps(json_serialized[0])
return Response(data)
Thanks for the help #miki275 :)