Question

import dataset

class db(object):
    _db_connection = None
    _db_cur = None

    def __init__(self):
        self._db_connection = dataset.connect(path_to_database)

    def __del__(self):
        self._db_connection.executable.close()

在上面的代码中，我创建了一个连接到AWS上现有数据库的类。有没有办法可以检查连接是否已经打开，如果是，返回现有连接而不是打开新连接？

Answer 1

您可以使用描述符：

class DBConn(object):
    conn = None

    def __get__(self, instance, owner):
        if instance is None:
            return self
        if self.conn is None or self.conn.closed():
            # Since this is a class attribute, it is shared by all instances
            self.conn = dataset.connect(path_to_database)
        return self.conn

    def __delete__(self, instance):
        self.conn.executable.close()
        self.conn = None

然后将其用作财产：

class DB(object):
    connection = DBConn()

db = DB()
db.connection.do_something()  # Opens a new connections
other_db = DB()
other_db.connection.do_something_else()  # Reuses same connection
del db.connection  # Closes the connection
other_db.connection.another_thing()  # Reopens the connection

Answer 2

它被称为Singleton模式看看： http://python-3-patterns-idioms-test.readthedocs.io/en/latest/Singleton.html

class OnlyOne(object):
    class __OnlyOne:
        def __init__(self):
            self.val = None
        def __str__(self):
            return `self` + self.val
    instance = None
    def __new__(cls): # __new__ always a classmethod
        if not OnlyOne.instance:
            OnlyOne.instance = OnlyOne.__OnlyOne()
        return OnlyOne.instance
    def __getattr__(self, name):
        return getattr(self.instance, name)
    def __setattr__(self, name):
        return setattr(self.instance, name)

Answer 3

在连接时，如果驱动程序无法连接，则可能会出现异常

因此您需要将您的连接呼叫包装到

中

class db(object):
    _db_connection = None
    _db_cur = None

    def __init__(self):
       try:
           self._db_connection = dataset.connect(path_to_database)
       except WhateverExceptionYourDBDriverThrowsOnError:
           pass

    def __del__(self):
        if self._db_connection:
            self._db_connection.executable.close()

你没说什么驱动程序，你使用什么数据库，所以这是通用代码。您需要将Exception类型替换为驱动程序抛出的正确类型。

Answer 4

db.local.conn.closed # return True or False

我在此post

中使用它

在python中打开新数据库之前检查是否存在与数据库的连接

4 个答案: