Ужесточена валидация публикации choice-заданий, синхронизировано поле completed_at со статусом курса и добавлена транзакционная защита от гонок при сохранении single_choice ответа

Author: Toksi86

courses/models/answers.py

@@ -1,6 +1,6 @@
 from django.conf import settings
 from django.core.exceptions import ValidationError
-from django.db import models
+from django.db import models, transaction
 from django.utils import timezone
 
 from files.models import UserFile
@@ -203,8 +203,12 @@ def clean(self):
             raise ValidationError(errors)
 
     def save(self, *args, **kwargs):
-        self.full_clean()
-        super().save(*args, **kwargs)
+        with transaction.atomic():
+            if self.answer_id:
+                # Serializes single_choice writes for one answer.
+                self.answer.__class__.objects.select_for_update().get(pk=self.answer_id)
+            self.full_clean()
+            super().save(*args, **kwargs)
 
 
 class UserTaskAnswerFile(models.Model):

courses/models/content.py

@@ -336,9 +336,12 @@ def clean(self):
                 CourseTaskAnswerType.SINGLE_CHOICE,
                 CourseTaskAnswerType.MULTIPLE_CHOICE,
             )
-            and self.pk
         ):
-            correct_count = self.options.filter(is_correct=True).count()
+            correct_count = (
+                self.options.filter(is_correct=True).count()
+                if self.pk
+                else 0
+            )
             if correct_count == 0:
                 errors["status"] = (
                     "Нельзя опубликовать тестовое задание без правильного варианта."

courses/models/course.py

@@ -179,4 +179,7 @@ def save(self, *args, **kwargs):
             if not self.completed_at:
                 self.completed_at = timezone.now()
 
+        if self.status != CourseContentStatus.COMPLETED:
+            self.completed_at = None
+
         super().save(*args, **kwargs)