变更项目架构，提高扩展性

backend/core/database.py

@@ -0,0 +1,38 @@
+from sqlalchemy import create_engine, MetaData, Table
+from pgvector.sqlalchemy import Vector
+from .config import settings
+
+class Database:
+    """
+    数据库单例类
+    负责初始化连接池并反射加载现有的表结构
+    """
+    def __init__(self):
+        # 1. 创建引擎
+        # pool_pre_ping=True 用于解决数据库连接长时间空闲后断开的问题
+        self.engine = create_engine(settings.DATABASE_URL, pool_pre_ping=True)
+        
+        # 2. 注册 pgvector 类型
+        # 这是为了让 SQLAlchemy 反射机制能识别数据库中的 'vector' 类型
+        self.engine.dialect.ischema_names['vector'] = Vector
+        
+        self.metadata = MetaData()
+        self.tasks = None
+        self.queue = None
+        self.chunks = None
+        
+        self._reflect_tables()
+
+    def _reflect_tables(self):
+        """自动从数据库加载表定义"""
+        try:
+            # autoload_with 会查询数据库元数据，自动填充 Column 信息
+            self.tasks = Table('crawl_tasks', self.metadata, autoload_with=self.engine)
+            self.queue = Table('crawl_queue', self.metadata, autoload_with=self.engine)
+            self.chunks = Table('knowledge_chunks', self.metadata, autoload_with=self.engine)
+            print("[INFO] Database tables reflected successfully.")
+        except Exception as e:
+            print(f"[ERROR] Failed to reflect tables: {e}")
+
+# 全局数据库实例
+db = Database()