我是否需要刷新 sqlalchemy 连接对象才能将数据插入到新创建的表中？

Question

我是 sqlalchemy 的初学者。

我在_core.py

中的连接功能

from sqlalchemy import create_engine
from methodtools import lru_cache


@lru_cache(maxsize=16)
def get_engine(db="homelan"):
    qs = 'mysql+pymysql://user:pwd@localhost/{db}'.format(db=db)
    engine = create_engine(qs)
    connection = engine.connect()
    return engine, connection

如果我创建的特定主机的表不存在，则在我的代码中。如下图：

server_status.py

class HostStatusManager(object):

    keep_record = 10 # days

    """This class contains methods to manage the status of the host
    registered in database for supervision or monitoring purpose.
    """

    def __init__(self, ip_address):
        super(HostStatusManager, self).__init__()
        self._ip = ip_address
        engine, connection = _core.get_engine()
        self._engine = engine
        self._connection = connection
        self._host_table = None
        self._host_table_name = None
        if not self.host_status_table_exists():
            self._host_table = self._create_table()



    def get_status(self):
        """Gets the latest status of the host whether online or offline.
        """
        columns = self._host_table.columns
        print("Cols: ".format(columns))
        select_field = getattr(columns, "status")
        query = db.select(
                [select_field]
            ).order_by(
                db.desc(
                    getattr(columns, "id")
                    )
                ).limit(1)
        _log.debug(query)
        ResultProxy = self._connection.execute(query)
        ResultSet = ResultProxy.fetchall()
        if ResultSet:
            return ResultSet[0][0]
        _log.warning("No existing status found from {0}.".format(
            self._host_table
            )
        )

    def set_status(self, data):
        query = db.insert(self._host_table).values(**data)
        results = self._connection.execute(query)

如果我直接调用 set_status 它工作正常，但 get_status 抛出错误说：

pymysql.err.InternalError: (1412, '表定义已更改， 请重试交易'）

Answer 1

您不应该使用 lru 缓存来存储连接，而应该使用引擎的内置连接池。然后，每次需要与数据库通信时，向引擎请求连接，并在完成后关闭连接。默认情况下，引擎将有一个大小为 5 的池。

from sqlalchemy import create_engine

def get_engine(db="homelan"):
    qs = 'mysql+pymysql://user:pwd@localhost/{db}'.format(db=db)
    engine = create_engine(qs)
    return engine

class HostStatusManager(object):

    keep_record = 10 # days

    """This class contains methods to manage the status of the host
    registered in database for supervision or monitoring purpose.
    """

    def __init__(self, ip_address):
        super(HostStatusManager, self).__init__()
        self._ip = ip_address
        engine, connection = _core.get_engine()
        self._engine = engine
        self._host_table = None
        self._host_table_name = None
        if not self.host_status_table_exists():
            self._host_table = self._create_table()



    def get_status(self):
        """Gets the latest status of the host whether online or offline.
        """
        columns = self._host_table.columns
        print("Cols: ".format(columns))
        select_field = getattr(columns, "status")
        query = db.select(
                [select_field]
            ).order_by(
                db.desc(
                    getattr(columns, "id")
                    )
                ).limit(1)
        _log.debug(query)
        connection = self._engine.connect()
        try:
            ResultProxy = connection.execute(query)
            ResultSet = ResultProxy.fetchall()
            if ResultSet:
                return ResultSet[0][0]
            _log.warning("No existing status found from {0}.".format(
                self._host_table
                )
            )
        finally:
            connection.close()

    def set_status(self, data):
        query = db.insert(self._host_table).values(**data)
        connection = self._engine.connect()
        try:
            results = connection.execute(query)
        finally:
            connection.close()