uncloud/uncloud/uncloud_pay/serializers.py

from django.contrib.auth import get_user_model
from rest_framework import serializers
from .models import Bill, Payment

class BillSerializer(serializers.ModelSerializer):
    class Meta:
        model = Bill
        fields = ['owner', 'amount', 'due_date', 'creation_date', 'starting_date', 'ending_date', 'paid']

class PaymentSerializer(serializers.ModelSerializer):
    class Meta:
        model = Payment
        fields = ['owner', 'amount', 'source', 'timestamp']

class UserSerializer(serializers.ModelSerializer):
    class Meta:
        model = get_user_model()
        fields = ['username', 'email']

    def get_balance(self, obj):
        return 666