修复：PostgreSQL 语法适配 + UUID 自动生成

backend/app/db/base.py

@@ -3,6 +3,7 @@
 所有子图的数据操作都用这个，避免重复代码
 """
 import json
+import uuid
 from typing import Any, List, Dict, Optional
 from dataclasses import dataclass, asdict
 
@@ -53,7 +54,10 @@ class BaseRepository:
     async def insert(self, entity: BaseEntity) -> str:
         """插入单个实体，返回 ID"""
         data = entity.to_dict()
-        data.pop('id', None)  # 如果 id 是自增的
+        
+        # 确保有 ID
+        if not data.get('id'):
+            data['id'] = str(uuid.uuid4())
         
         if not data:
             raise ValueError("实体数据为空")
@@ -71,7 +75,7 @@ class BaseRepository:
         async with self.conn.cursor() as cur:
             await cur.execute(sql, values)
             row = await cur.fetchone()
-            return row[self.id_column] if row else None
+            return row[self.id_column] if row else data['id']
     
     async def update(self, entity_id: str, data: Dict[str, Any]) -> bool:
         """更新实体"""