完善审计日志展示与导出权限

backend/app/crud/audit.py

@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 import uuid
 from typing import Sequence
 
@@ -65,8 +67,3 @@ async def list_logs(
 async def get_log(db: AsyncSession, log_id: uuid.UUID) -> AuditLog | None:
     result = await db.execute(select(AuditLog).where(AuditLog.id == log_id))
     return result.scalar_one_or_none()
-
-
-async def delete_log(db: AsyncSession, log: AuditLog) -> None:
-    await db.delete(log)
-    await db.commit()

backend/app/crud/study.py

@@ -121,11 +121,10 @@ async def delete(db: AsyncSession, study_id: uuid.UUID) -> None:
     from app.models.study_monitoring_strategy import StudyMonitoringStrategy
     from app.models.study_center_confirm import StudyCenterConfirm
     
-    # 按依赖关系顺序删除关联数据
-    # 1. 删除审计日志
-    await db.execute(sa_delete(AuditLog).where(AuditLog.study_id == study_id))
+    # 按依赖关系顺序删除关联数据。审计日志必须保留，只解除项目外键，避免硬删除项目时破坏审计链。
+    await db.execute(sa_update(AuditLog).where(AuditLog.study_id == study_id).values(study_id=None))
     
-    # 2. 删除FAQ相关（可能有依赖关系）
+    # 1. 删除FAQ相关（可能有依赖关系）
     await db.execute(sa_delete(FaqReply).where(FaqReply.study_id == study_id))
     await db.execute(sa_delete(FaqItem).where(FaqItem.study_id == study_id))
     await db.execute(sa_delete(FaqCategory).where(FaqCategory.study_id == study_id))