[连接数据库](%E8%BF%9E%E6%8E%A5%E6%95%B0%E6%8D%AE%E5%BA%93.md) [链式操作](%E9%93%BE%E5%BC%8F%E6%93%8D%E4%BD%9C.md) [构造器](%E6%9E%84%E9%80%A0%E5%99%A8.md)