Can't create() nested relationship with DRF - django

Question

This is the first time I'm working with DRF.
My models:
class ServiceCategory(models.Model):
category = models.CharField(max_length=24)
class Service(models.Model):
service = models.CharField(max_length=24)
category = models.ForeignKey('ServiceCategory')
Their serializers:
class ServiceCategorySerializer(serializers.ModelSerializer):
class Meta:
model = ServiceCategory
fields = ('id', 'category')
class ServiceSerializer(serializers.ModelSerializer):
category = ServiceCategorySerializer()
class Meta:
model = Service
fields = ('service', 'category')
def create(self, data):
return Service.objects.create(**data)
And the view:
elif request.method == 'POST':
serializer = ServiceSerializer(data=request.data)
print(serializer.initial_data) # To debug the contents of the request
if serializer.is_valid():
serializer.save()
return Response(serializer.data, status=status.HTTP_201_CREATED)
return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)
Initially, before I added the nested category to the ServiceSerializer, I had no problem creating new Services. The print(serializer.initial_data) outputs <QueryDict: {'category': ['1'], 'service': ['EC2']}> so obviously I'm supplying the category to the request but I'm getting "category" : ["This field is required"] errors.
So I'm thinking the problem might be with my create(self, data) method in the ServiceSerializer but I'm unable to put a finger on what exactly is wrong with it.
What have I missed?
UPDATE
Without the ServiceCategorySerializer in the ServiceSerializer, and the view being:
elif request.method == 'POST':
serializer = ServiceSerializer(data=request.data)
print(serializer.initial_data) # for debugging
if serializer.is_valid():
print(serializer.data) # for debugging
serializer.initial_data returns <QueryDict: {'category': ['1'], 'service': ['EC2']}>
and
serializer.data returns {'service': 'EC2', 'category': 1} so I assume the contents of serializer.data are what will get passed to the create() method of the ServiceSerializer. By itself, it works, but when I include the ServiceCategorySerializer inside it, the POST doesn't go through and I get the same annoying "category" : ["This field is required"]
I've been stuck with this for over 6 hours now. What is going on???

Answer 1

I have a full working example - of what you wanna achieve - using just information that I found in this thread:
Models:
from __future__ import unicode_literals
from django.db import models
class ServiceCategory(models.Model):
category = models.CharField(max_length=24)
class Service(models.Model):
service = models.CharField(max_length=24)
category = models.ForeignKey('ServiceCategory')
Serializers:
from rest_framework import serializers
from nestedd.models import ServiceCategory, Service
class ServiceCategorySerializer(serializers.ModelSerializer):
class Meta:
model = ServiceCategory
fields = ('id', 'category')
class ServiceSerializer(serializers.ModelSerializer):
category = ServiceCategorySerializer()
class Meta:
model = Service
fields = ('service', 'category')
def create(self, validated_data):
category_data = validated_data.pop('category')
# 'created' will be True if no existing category matches
category, created = ServiceCategory.objects.get_or_create(**category_data)
return Service.objects.create(category=category, **validated_data)
Views:
# Create your views here.
from rest_framework import viewsets
from nestedd.models import Service
from nestedd.serializers import ServiceSerializer
class ServiceViewSet(viewsets.ModelViewSet):
queryset = Service.objects.all()
serializer_class = ServiceSerializer
urls:
from rest_framework.routers import DefaultRouter
from nestedd.views import ServiceViewSet
router = DefaultRouter()
router.register(r'nested', ServiceViewSet, base_name='service')
urlpatterns = router.urls
app urls:
url(r'^api/v2/', include('nestedd.urls')),
And this how my postman look likes:
THE PROBLEM - POST DATA FORMAT
Probably you made a wrong POST query - if you want to use nested serializer, like this:
category = ServiceCategorySerializer()
In some other serializer, you must know that first field name is attached to the parent serializer, eg.:
{
"service_name": "test",
"category": ...
}
And what should be placed in category field? Well - an object, because you tell that this field is another serializer, if object then:
{
"service_name": "test",
"category": {
"category": "some_category"
}
}
And in this object you specify the fields for the model which is described by inner serializer, so basically, when you pass only the "id" -> it obvious that ServiceCategory cannot be created, beacause the category field on model ServiceCategory - is required.
ANOTHER NOTE: EXISITING VS. NON EXISITNG CATEGORY
You will have problems with handling existing/non-existing category;
Basically you should make category field unique on ServiceCategory, and in post on ServiceViewSet - check if category exists (if so take it and assign to the Service object - if no - create a category) - in this scenario you will not need to pass category id each time. And handle it when id - does not exists.

Answer 2

When POSTing a service, the category field must contain a PK, i.e. an integer. Your category field in serializer.initial_data contains a list with a string.
BTW1: your service field also has a list when your model expects a string (CharField). This might also be a problem.
BTW2: No need to override your serializer's create in your case.

Answer 3

As stated in the docs, you should implement the create() method in a slightly different way, saving the category first if it doesn't exist yet, and then passing it to the Service.objects.create() function, like this (untested):
def create(self, validated_data):
category_data = validated_data.pop('category')
# 'created' will be True if no existing category matches
category, created = ServiceCategory.objects.get_or_create(**category_data)
return Service.objects.create(category=category, **validated_data)