fix N+1 query

problemset/views/oj.py

@@ -1,4 +1,4 @@
-from django.db.models import Q, Avg
+from django.db.models import Q, Avg, Count
 from django.utils import timezone
 
 from utils.api import APIView, validate_serializer
@@ -306,13 +306,13 @@ class ProblemSetUserProgressAPI(APIView):
         except ProblemSet.DoesNotExist:
             return self.error("题单不存在")
 
-        # 获取所有参与该题单的用户进度
-        progresses = ProblemSetProgress.objects.filter(problemset=problem_set)
+        # 获取所有参与该题单的用户进度，使用 select_related 预加载用户信息
+        progresses = ProblemSetProgress.objects.filter(problemset=problem_set).select_related('user')
         
         # 班级过滤
         class_name = request.GET.get("class_name", "").strip()
         if class_name:
-            progresses = progresses.filter(user_username__icontains=class_name)
+            progresses = progresses.filter(user__username__icontains=class_name)
         
         # 排序
         progresses = progresses.order_by(
@@ -320,9 +320,43 @@ class ProblemSetUserProgressAPI(APIView):
         )
         
         # 计算统计数据（基于所有数据，而非分页数据）
-        total_count = progresses.count()
-        completed_count = progresses.filter(is_completed=True).count()
-        avg_progress = progresses.aggregate(avg=Avg("progress_percentage"))["avg"] or 0
+        # 使用一次查询获取所有统计数据
+        stats = progresses.aggregate(
+            total=Count('id'),
+            completed=Count('id', filter=Q(is_completed=True)),
+            avg_progress=Avg("progress_percentage")
+        )
+        total_count = stats['total']
+        completed_count = stats['completed']
+        avg_progress = stats['avg_progress'] or 0
+        
+        # 获取分页参数，用于预先收集当前页需要的问题ID
+        try:
+            limit = int(request.GET.get("limit", "10"))
+        except ValueError:
+            limit = 10
+        try:
+            offset = int(request.GET.get("offset", "0"))
+        except ValueError:
+            offset = 0
+        if offset < 0:
+            offset = 0
+        
+        # 只从当前页的数据中收集问题ID，避免遍历所有记录
+        paginated_progresses = list(progresses[offset:offset + limit])
+        all_problem_ids = set()
+        for progress in paginated_progresses:
+            if progress.progress_detail:
+                all_problem_ids.update(progress.progress_detail.keys())
+        
+        # 批量加载当前页所需的问题
+        problems_dict = {}
+        if all_problem_ids:
+            problems = Problem.objects.filter(id__in=all_problem_ids).only('id', '_id', 'title')
+            problems_dict = {str(problem.id): problem for problem in problems}
+        
+        # 将预加载的问题字典存储到 request 中，供序列化器使用
+        request._problems_dict_cache = problems_dict
         
         # 使用分页
         data = self.paginate_data(request, progresses, ProblemSetProgressSerializer)