Can't POST after extending User model fields in Django REST - django

Question

I am able to extend User model fields and I can see API browser with these fields and inputs, but when I try to POST a new user I got this error:
'signup' is an invalid keyword argument for this function
or if I change in serializers.py
User.objects.create(**validated_data)
to
SignUp.objects.create(**validated_data)
I got
'username' is an invalid keyword argument for this function
serializers.py
from rest_framework import serializers
from django.contrib.auth.models import User
class UserSerializer(serializers.ModelSerializer):
city = serializers.CharField(source='signup.city')
class Meta:
model = User
fields = ('username', 'first_name', 'last_name', 'city')
def create(self, validated_data):
return User.objects.create(**validated_data)
models.py
from django.contrib.gis.db import models
from django.contrib.auth.models import User
class SignUp(models.Model):
user=models.OneToOneField(User, primary_key=True)
city = models.CharField(max_length=50, blank=True)
def __unicode__(self):
return self.first_name

Answer 1

You'll want to do this through the related_name field in your model and then you can reference it on the serializer.
class SignUp(models.Model):
user=models.OneToOneField(User, primary_key=True, related_name='signup') # <---
I don't think you can flatten nested fields into the parent model's serializer.
You can do a nested field:
class UserSerializer(serializers.ModelSerializer):
city = serializers.CharField(source='signup')
If you access it via the JSON path, you'll get an object like:
{
url: "localhost:8000/users/1",
username: "foo",
email: "foo#example.com",
signup: {
city: "Seattle"
}
}