refactor(problem): 标签创建逻辑收敛到 services.resolve_tags

原本 4 处题目保存逻辑各自复制了一份 get-or-create，且大小写敏感、有竞态。

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

problem/services.py

@@ -0,0 +1,52 @@
+from django.core.cache import cache
+from django.db import IntegrityError
+
+from utils.constants import CacheKey
+
+from .models import ProblemTag
+
+
+def clear_tag_cache():
+    """标签列表接口按 keyword 分键缓存，标签一变就整批清掉"""
+    cache.delete_pattern(f"{CacheKey.problem_tags}:*")
+
+
+def find_tags(names):
+    """按名字大小写不敏感查已有标签，查不到就跳过，不创建"""
+    tags = []
+    seen = set()
+    for raw in names:
+        name = (raw or "").strip()
+        if not name or name.lower() in seen:
+            continue
+        seen.add(name.lower())
+        tag = ProblemTag.objects.filter(name__iexact=name).first()
+        if tag is not None:
+            tags.append(tag)
+    return tags
+
+
+def resolve_tags(names):
+    """把前端传来的标签名解析成 ProblemTag：去空格、大小写不敏感复用已有标签，没有才新建"""
+    tags = []
+    seen = set()
+    created = False
+    for raw in names:
+        name = (raw or "").strip()
+        if not name or name.lower() in seen:
+            continue
+        seen.add(name.lower())
+        tag = ProblemTag.objects.filter(name__iexact=name).first()
+        if tag is None:
+            try:
+                tag = ProblemTag.objects.create(name=name)
+                created = True
+            except IntegrityError:
+                # 并发下另一个请求刚建好同名标签，回查复用
+                tag = ProblemTag.objects.filter(name__iexact=name).first()
+                if tag is None:
+                    continue
+        tags.append(tag)
+    if created:
+        clear_tag_cache()
+    return tags

problem/views/admin.py

@@ -19,7 +19,7 @@ from utils.api import APIError, APIView, CSRFExemptAPIView, validate_serializer
 from utils.openai import get_ai_client
 from utils.shortcuts import natural_sort_key, rand_str
 
-from ..models import Problem, ProblemTag
+from ..models import Problem
 from ..serializers import (
     AddContestProblemSerializer,
     ContestProblemMakePublicSerializer,
@@ -32,6 +32,7 @@ from ..serializers import (
     SQLTestCasePreviewSerializer,
     TestCaseUploadForm,
 )
+from ..services import resolve_tags
 from ..utils import generate_sql_display
 
 
@@ -248,12 +249,7 @@ class ProblemAPI(ProblemBase):
         data["created_by"] = request.user
         problem = Problem.objects.create(**data)
 
-        for item in tags:
+        problem.tags.set(resolve_tags(tags))
-            try:
-                tag = ProblemTag.objects.get(name=item)
-            except ProblemTag.DoesNotExist:
-                tag = ProblemTag.objects.create(name=item)
-            problem.tags.add(tag)
         return self.success(ProblemAdminSerializer(problem).data)
 
     @problem_permission_required
@@ -310,14 +306,7 @@ class ProblemAPI(ProblemBase):
             setattr(problem, k, v)
         problem.save()
 
-        problem.tags.remove(*problem.tags.all())
+        problem.tags.set(resolve_tags(tags))
-        for tag in tags:
-            try:
-                tag = ProblemTag.objects.get(name=tag)
-            except ProblemTag.DoesNotExist:
-                tag = ProblemTag.objects.create(name=tag)
-            problem.tags.add(tag)
-
         return self.success()
 
     @problem_permission_required
@@ -364,12 +353,7 @@ class ContestProblemAPI(ProblemBase):
         data["created_by"] = request.user
         problem = Problem.objects.create(**data)
 
-        for item in tags:
+        problem.tags.set(resolve_tags(tags))
-            try:
-                tag = ProblemTag.objects.get(name=item)
-            except ProblemTag.DoesNotExist:
-                tag = ProblemTag.objects.create(name=item)
-            problem.tags.add(tag)
         return self.success(ProblemAdminSerializer(problem).data)
 
     def get(self, request):
@@ -434,13 +418,7 @@ class ContestProblemAPI(ProblemBase):
             setattr(problem, k, v)
         problem.save()
 
-        problem.tags.remove(*problem.tags.all())
+        problem.tags.set(resolve_tags(tags))
-        for tag in tags:
-            try:
-                tag = ProblemTag.objects.get(name=tag)
-            except ProblemTag.DoesNotExist:
-                tag = ProblemTag.objects.create(name=tag)
-            problem.tags.add(tag)
         return self.success()
 
     def delete(self, request):