初始化提交，包含完整的邮件系统代码

app/models/attachment.py

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+from sqlalchemy import Column, Integer, String, DateTime, ForeignKey, LargeBinary
+from sqlalchemy.orm import relationship
+from datetime import datetime
+import os
+
+from . import Base
+
+class Attachment(Base):
+    """附件模型"""
+    __tablename__ = 'attachments'
+
+    id = Column(Integer, primary_key=True)
+    email_id = Column(Integer, ForeignKey('emails.id'), nullable=False, index=True)
+    filename = Column(String(255), nullable=False)
+    content_type = Column(String(100), nullable=True)
+    size = Column(Integer, nullable=False, default=0)
+    storage_path = Column(String(500), nullable=True)  # 用于文件系统存储
+    content = Column(LargeBinary, nullable=True)  # 用于小型附件的直接存储
+    created_at = Column(DateTime, default=datetime.utcnow)
+    
+    # 关联关系
+    email = relationship("Email", back_populates="attachments")
+    
+    @property
+    def is_stored_in_fs(self):
+        """判断附件是否存储在文件系统中"""
+        return bool(self.storage_path and not self.content)
+    
+    def save_to_filesystem(self, content, base_path):
+        """将附件保存到文件系统"""
+        # 确保目录存在
+        os.makedirs(base_path, exist_ok=True)
+        
+        # 创建文件路径
+        file_path = os.path.join(
+            base_path, 
+            f"{self.email_id}_{self.id}_{self.filename}"
+        )
+        
+        # 写入文件
+        with open(file_path, 'wb') as f:
+            f.write(content)
+        
+        # 更新对象属性
+        self.storage_path = file_path
+        self.size = len(content)
+        self.content = None  # 清空内存中的内容
+        
+        return file_path
+    
+    def get_content(self, attachments_dir=None):
+        """获取附件内容，无论是从数据库还是文件系统"""
+        if self.content:
+            return self.content
+            
+        if self.storage_path and os.path.exists(self.storage_path):
+            with open(self.storage_path, 'rb') as f:
+                return f.read()
+                
+        return None
+        
+    def to_dict(self):
+        """转换为字典，用于API响应"""
+        return {
+            "id": self.id,
+            "email_id": self.email_id,
+            "filename": self.filename,
+            "content_type": self.content_type,
+            "size": self.size,
+            "created_at": self.created_at.isoformat() if self.created_at else None
+        }