Fix a few errors on preview billing rework

Another WIP commit to sync with laptop, do not forget to rebase!

uncloud/uncloud_pay/helpers.py

@@ -5,6 +5,8 @@ from rest_framework.viewsets import GenericViewSet
 from django.db.models import Q
 from .models import Bill, Payment, PaymentMethod, Order
 from django.utils import timezone
+from django.core.exceptions import ObjectDoesNotExist
+from dateutil.relativedelta import relativedelta
 
 def sum_amounts(entries):
     return reduce(lambda acc, entry: acc + entry.amount, entries, 0)

uncloud/uncloud_pay/migrations/0011_auto_20200229_1459.py

@@ -0,0 +1,21 @@
+# Generated by Django 3.0.3 on 2020-02-29 14:59
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('uncloud_pay', '0010_merge_20200228_1303'),
+    ]
+
+    operations = [
+        migrations.RemoveField(
+            model_name='order',
+            name='one_time_price',
+        ),
+        migrations.RemoveField(
+            model_name='order',
+            name='recurring_price',
+        ),
+    ]

uncloud/uncloud_pay/serializers.py

@@ -10,7 +10,7 @@ from uncloud_vm.models import VMProduct
 class BillSerializer(serializers.ModelSerializer):
     class Meta:
         model = Bill
-        fields = ['owner', 'amount', 'due_date', 'creation_date',
+        fields = ['owner', 'total', 'due_date', 'creation_date',
                 'starting_date', 'ending_date']
 
 class PaymentSerializer(serializers.ModelSerializer):