Fix submission list API performance: N+1 queries, missing indexes, and in-memory pagination

- Add select_related("user") in update_score() to eliminate N+1 on rating.user.role
- Return QuerySet directly from list_submissions so @paginate works at DB level
- Defer html/css/js fields in list queries to reduce data transfer
- Add db_index on flag field for filtered queries
- Add select_related("task", "user") to get_submission endpoint
- Replace manual list() serialization with resolve_* methods on SubmissionOut

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

submission/api.py

@@ -56,7 +56,9 @@ def list_submissions(request, filters: SubmissionFilter = Query(...)):
     """
     获取提交列表，支持按任务和用户过滤
     """
-    submissions = Submission.objects.select_related("task", "user")
+    submissions = Submission.objects.select_related("task", "user").defer(
+        "html", "css", "js"
+    )
 
     if filters.task_id:
         task = get_object_or_404(Task, id=filters.task_id)
@@ -76,12 +78,7 @@ def list_submissions(request, filters: SubmissionFilter = Query(...)):
     )
     submissions = submissions.annotate(my_score=user_rating_subquery)
 
-    def get_submission_data(submission):
-        """从 submission 对象构建 SubmissionOut 数据"""
-        my_score = getattr(submission, "my_score", None) or 0
-        return SubmissionOut.list(submission, {submission.id: my_score})
-
-    return [get_submission_data(submission) for submission in submissions]
+    return submissions
 
 
 @router.get("/{submission_id}", response=SubmissionOut)
@@ -90,10 +87,11 @@ def get_submission(request, submission_id: UUID):
     """
     获取单个提交的详细信息
     """
-    submission = get_object_or_404(Submission, id=submission_id)
+    submission = get_object_or_404(
+        Submission.objects.select_related("task", "user"), id=submission_id
+    )
     rating = (
-        Rating.objects.select_related("user", "submission")
-        .filter(user=request.user, submission=submission)
+        Rating.objects.filter(user=request.user, submission=submission)
         .first()
     )
     return SubmissionOut.get(submission, rating)

submission/migrations/0005_add_flag_index.py

@@ -0,0 +1,18 @@
+# Generated by Django 6.0.1 on 2026-03-09 10:24
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('submission', '0004_submission_flag'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='submission',
+            name='flag',
+            field=models.CharField(blank=True, choices=[('red', '值得展示'), ('blue', '需要讲解'), ('green', '优秀作品'), ('yellow', '需要改进')], db_index=True, default=None, max_length=10, null=True, verbose_name='标记'),
+        ),
+    ]

submission/models.py

@@ -44,6 +44,7 @@ class Submission(TimeStampedModel):
         null=True,
         blank=True,
         default=None,
+        db_index=True,
         verbose_name="标记",
     )
 
@@ -63,7 +64,7 @@ class Submission(TimeStampedModel):
         """
         更新当前Submission的分数
         """
-        ratings = self.ratings.all()
+        ratings = list(self.ratings.select_related("user").all())
 
         super_score = 0.0
         admin_score = 0.0
@@ -77,13 +78,13 @@ class Submission(TimeStampedModel):
             else:
                 normal_score += rating.score
 
-        if ratings.exists():
+        if ratings:
             total_score = super_score * 0.5 + admin_score * 0.3 + normal_score * 0.2
-            self.score = total_score / ratings.count()
+            self.score = total_score / len(ratings)
         else:
             self.score = 0.0
 
-        self.save()
+        self.save(update_fields=["score"])
 
     def save(self, *args, **kwargs):
         super().save(*args, **kwargs)

submission/schemas.py

@@ -20,7 +20,7 @@ class SubmissionOut(Schema):
     task_title: str
     task_type: Literal["tutorial", "challenge"]
     score: float
-    my_score: int
+    my_score: int = 0
     html: Optional[str] = None
     css: Optional[str] = None
     js: Optional[str] = None
@@ -30,22 +30,40 @@ class SubmissionOut(Schema):
     modified: str
 
     @staticmethod
-    def list(submission, rating_dict):
-        return {
-            "id": submission.id,
-            "userid": submission.user.id,
-            "username": submission.user.username,
-            "task_id": submission.task.id,
-            "task_display": submission.task.display,
-            "task_title": submission.task.title,
-            "task_type": submission.task.task_type,
-            "score": submission.score,
-            "my_score": rating_dict.get(submission.id, 0),
-            "conversation_id": submission.conversation_id,
-            "flag": submission.flag,
-            "created": submission.created.isoformat(),
-            "modified": submission.modified.isoformat(),
-        }
+    def resolve_userid(obj):
+        return obj.user.id
+
+    @staticmethod
+    def resolve_username(obj):
+        return obj.user.username
+
+    @staticmethod
+    def resolve_task_id(obj):
+        return obj.task.id
+
+    @staticmethod
+    def resolve_task_display(obj):
+        return obj.task.display
+
+    @staticmethod
+    def resolve_task_title(obj):
+        return obj.task.title
+
+    @staticmethod
+    def resolve_task_type(obj):
+        return obj.task.task_type
+
+    @staticmethod
+    def resolve_my_score(obj):
+        return getattr(obj, "my_score", None) or 0
+
+    @staticmethod
+    def resolve_created(obj):
+        return obj.created.isoformat()
+
+    @staticmethod
+    def resolve_modified(obj):
+        return obj.modified.isoformat()
 
     @staticmethod
     def get(submission, rating):