diff --git a/python_core/api/auth_api.py b/python_core/api/auth_api.py
index 2854671..f1b40f4 100644
--- a/python_core/api/auth_api.py
+++ b/python_core/api/auth_api.py
@@ -35,11 +35,12 @@ class AuthAPI:
         """
         try:
             # 创建注册请求对象
+            display_name = data.get("display_name", "") or ""
             request = RegisterRequest(
                 username=data.get("username", "").strip(),
                 email=data.get("email", "").strip(),
                 password=data.get("password", ""),
-                display_name=data.get("display_name", "").strip() or None
+                display_name=display_name.strip() or None
             )
             
             # 执行注册
diff --git a/python_core/database/user_postgres.py b/python_core/database/user_postgres.py
index 866563c..c678fdf 100644
--- a/python_core/database/user_postgres.py
+++ b/python_core/database/user_postgres.py
@@ -161,6 +161,20 @@ PostgreSQL 驱动 psycopg2 未安装。请安装：
                     ADD COLUMN avatar_url TEXT DEFAULT ''
                 """)
 
+            # 检查 last_login 字段是否存在
+            cursor.execute("""
+                SELECT column_name
+                FROM information_schema.columns
+                WHERE table_name = 'users' AND column_name = 'last_login'
+            """)
+
+            if not cursor.fetchone():
+                logger.info("Adding last_login column to users table")
+                cursor.execute("""
+                    ALTER TABLE users
+                    ADD COLUMN last_login TIMESTAMP
+                """)
+
         except Exception as e:
             logger.error(f"Failed to migrate user table: {e}")
             raise e
@@ -251,12 +265,12 @@ PostgreSQL 驱动 psycopg2 未安装。请安装：
                             'username': row['username'],
                             'email': row['email'],
                             'password_hash': row['password_hash'],
-                            'display_name': row['display_name'],
-                            'avatar_url': row['avatar_url'],
+                            'display_name': row.get('display_name', row['username']),
+                            'avatar_url': row.get('avatar_url', ''),
                             'is_active': row['is_active'],
-                            'last_login': row['last_login'].isoformat() if row['last_login'] else None,
-                            'created_at': row['created_at'].isoformat() if row['created_at'] else None,
-                            'updated_at': row['updated_at'].isoformat() if row['updated_at'] else None
+                            'last_login': row.get('last_login').isoformat() if row.get('last_login') else None,
+                            'created_at': row.get('created_at').isoformat() if row.get('created_at') else None,
+                            'updated_at': row.get('updated_at').isoformat() if row.get('updated_at') else None
                         }
                     return None
 
@@ -286,12 +300,12 @@ PostgreSQL 驱动 psycopg2 未安装。请安装：
                             'username': row['username'],
                             'email': row['email'],
                             'password_hash': row['password_hash'],
-                            'display_name': row['display_name'],
-                            'avatar_url': row['avatar_url'],
+                            'display_name': row.get('display_name', row['username']),
+                            'avatar_url': row.get('avatar_url', ''),
                             'is_active': row['is_active'],
-                            'last_login': row['last_login'].isoformat() if row['last_login'] else None,
-                            'created_at': row['created_at'].isoformat() if row['created_at'] else None,
-                            'updated_at': row['updated_at'].isoformat() if row['updated_at'] else None
+                            'last_login': row.get('last_login').isoformat() if row.get('last_login') else None,
+                            'created_at': row.get('created_at').isoformat() if row.get('created_at') else None,
+                            'updated_at': row.get('updated_at').isoformat() if row.get('updated_at') else None
                         }
                     return None
 
@@ -321,12 +335,12 @@ PostgreSQL 驱动 psycopg2 未安装。请安装：
                             'username': row['username'],
                             'email': row['email'],
                             'password_hash': row['password_hash'],
-                            'display_name': row['display_name'],
-                            'avatar_url': row['avatar_url'],
+                            'display_name': row.get('display_name', row['username']),
+                            'avatar_url': row.get('avatar_url', ''),
                             'is_active': row['is_active'],
-                            'last_login': row['last_login'].isoformat() if row['last_login'] else None,
-                            'created_at': row['created_at'].isoformat() if row['created_at'] else None,
-                            'updated_at': row['updated_at'].isoformat() if row['updated_at'] else None
+                            'last_login': row.get('last_login').isoformat() if row.get('last_login') else None,
+                            'created_at': row.get('created_at').isoformat() if row.get('created_at') else None,
+                            'updated_at': row.get('updated_at').isoformat() if row.get('updated_at') else None
                         }
                     return None