How to use a single serializer to save multiple models

Problem : I’m unable to save the both models in database from a single serialzer.

Description : I’m using djoser auth library for registration and authentication. for that i’m using custom django auth user and mapped it with userprofile model. Since i’m using userprofile along with the django user, i have to use custom register serializer.

My Models

class CustomUser(AbstractUser):
    username = None
    email = models.EmailField(_("email address"), unique=True)
    
    USERNAME_FIELD = "email"
    REQUIRED_FIELDS = []
    
    objects = CustomUserManager()
    
class UserProfile(models.Model):
    user = models.OneToOneField(CustomUser, on_delete=models.CASCADE, related_name="userProfile")
    user_guid = models.UUIDField(
        default=uuid.uuid4,
        unique=True,
        editable=False
    )
    user_type = models.IntegerField(choices=UserType.choices(), default=UserType.BUYER)
    wallet_balance = models.FloatField()
    created_at = models.DateTimeField(auto_now=True)
    updated_at = models.DateTimeField(auto_now_add=True)
    
    class Meta:
        ordering = ['created_at' ]  # Corrected the ordering syntax

My Serializer

CustomUser = get_user_model()

class UserProfileSerializer(serializers.ModelSerializer):
    class Meta:
        model = UserProfile
        fields = ['user_guid', 'user_type', 'wallet_balance', 'created_at', 'updated_at']
        read_only_fields = ['user_guid', 'created_at', 'updated_at']

class CustomUserCreateSerializer(DjoserUserCreateSerializer):
    userProfile = UserProfileSerializer()

    class Meta:
        model = CustomUser
        fields = ['id', 'email', 'password', 'userProfile']
        extra_kwargs = {'password': {'write_only': True}}

    def create(self, validated_data):
        user_profile_data = validated_data.pop('userProfile')
        user = CustomUser.objects.create_user(**validated_data)
        

        UserProfile.objects.create(user=user, **user_profile_data)
        return user`


    `AUTH_USER_MODEL = 'users.CustomUser'
    DJOSER = {
    'SERIALIZERS': {
        'user_create': 'users.v1.serializers.CustomUserCreateSerializer',
        'user': 'users.v1.serializers.CustomUserCreateSerializer',
        'current_user': 'users.v1.serializers.CustomUserCreateSerializer',
    }
}

Error : raise ValueError( ValueError: Cannot assign “{‘user_type’: 1, ‘wallet_balance’: 0.0}”: “CustomUser.userProfile” must be a “UserProfile” instance.

1. You don't need to provide CustomUserCreateSerializer.Meta.extra_kwargs for password, because the "write_only" param already set in djoser.serializers.UserCreateSerializer;
2. You customized create method, like in this docs, but you need to customize validate method too.

from django.contrib.auth.password_validation import validate_password
from django.core import exceptions as django_exceptions
from djoser.serializers import UserCreateSerializer
from rest_framework import serializers
from rest_framework.settings import api_settings

from .models import UserProfile, CustomUser


class UserProfileSerializer(serializers.ModelSerializer):
    class Meta:
        model = UserProfile
        fields = ['user_guid', 'wallet_balance', 'created_at', 'updated_at']
        read_only_fields = ['user_guid', 'created_at', 'updated_at']


class CustomUserCreateSerializer(UserCreateSerializer):
    user_profile = UserProfileSerializer()

    class Meta:
        model = CustomUser
        fields = ['id', 'email', 'password', 'user_profile']

    def create(self, validated_data):
        profile_data = validated_data.pop('user_profile')
        user = CustomUser.objects.create_user(**validated_data)
        UserProfile.objects.create(user=user, **profile_data)
        return user

    def validate(self, attrs):
        profile_data = attrs.pop("user_profile")
        user = CustomUser(attrs)
        profile = UserProfile(user=user, **profile_data)
        password = attrs.get("password")
        try:
            validate_password(password, user)
        except django_exceptions.ValidationError as e:
            serializer_error = serializers.as_serializer_error(e)
            raise serializers.ValidationError(
                {"password": serializer_error[api_settings.NON_FIELD_ERRORS_KEY]}
            )
        attrs["user_profile"] = profile_data
        return attrs

this worked fine on my machine

• Notice that i removed user_type field, cause you didn't show it properly in your question (you can use it as you want).

python manage.py shell

Python 3.11.9 (tags/v3.11.9:de54cf5, Apr  2 2024, 10:12:12) [MSC v.1938 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
>>> from my_app.serializers import CustomUserCreateSerializer                                                     
>>> data = {"email": "lengthylyova@gmail.com", "password": "SomeInsanePassword123", "user_profile": {"wallet_balance": 0.0}}
>>> serializer = CustomUserCreateSerializer(data=data)
>>> serializer.is_valid(raise_exception=True) 
True
>>> serializer.save()
<CustomUser: lengthylyova@gmail.com>

UserProfile instance also created

sqlite3 db.sqlite3

sqlite> select * from my_app_userprofile;
1|3c6a03729d6a41f4b719b7a702b06507|0.0|2024-07-30 00:01:36.824563|2024-07-30 00:01:36.824563|1