SSCursor 处理大量数据

使用游标的好处是不会将查询结果全部都放入内存中，避免了占用大量的内存，会从存储块中读取记录，并且一条一条的返回来

class DbConnection(object):

    def __init__(self,host,port,username,password,db):

        self.host = host
        self.port = port
        self.username = username
        self.password = password
        self.db = db
        self.connection = None

    def __enter__(self):
        # 建立连接
        self.connection = pymysql.connect(host = self.host, port= self.port, user=self.username, passwd=self.password,
                                          db = self.db)
        #使用流式游标
        self.cursor = self.connection.cursor(pymysql.cursors.SSDictCursor)
        return  self.cursor

    def __exit__(self, exc_type, exc_val, exc_tb):
        self.connection.commit()
        self.cursor.close()
        self.connection.close()