参悟python元类(又称metaclass)系列实战(四)

z417 2020-11-17 14:07:55
Python 系列 参悟 又称 metaclass


写在前面

在上一章节参悟python元类(又称metaclass)系列实战(三)完成了users类users表的字段映射;
在继续丰富users类的操作之前, 我们花一章来完成mysql的链接;
有误的地方恳请大神指正下。

创建全局连接池, 以求避免频繁地打开和关闭数据库连接

  • 因为查询耗时, 计划引入异步, 即async/await(不懂没关系, 就当是普通代码, 只是调用方式特别而已)

    $ pip3 install aiomysql # 通过pip安装
    
  • 创建Mysql类, 定义静态方法createPool

    import aiomysql
    class Mysql:
    @staticmethod
    async def createPool():
    '''连接池由全局变量__pool存储,缺省情况下将编码设置为utf8,自动提交事务'''
    try:
    global __pool
    __pool = await aiomysql.create_pool(
    host='localhost', # mysql服务器地址
    port=3306, # mysql监听端口
    user='root', # mysql用户名
    password='passwd', # mysql密码
    db='ormdemo', # mysql实例名(database)
    charset='utf8', # 编码设置
    autocommit=True, # 自动提交insert/update/delete
    maxsize=10, # 连接池上限
    minsize=1 # 连接池下限
    )
    print('创建成功')
    except Exception as e:
    print(f'连接 mysql 出错:{e}')
    # 测试代码
    if __name__ == '__main__':
    import asyncio
    loop = asyncio.get_event_loop()
    loop.run_until_complete(Mysql.createPool())
    
  • Mysql类新增静态方法selectexecute

    @staticmethod
    async def select(sql, args, size=None):
    '''传入SQL语句和SQL参数
    @sql : sql语句
    @args: 条件值列表
    @size: 查询的结果集大小
    '''
    print(f'{sql} ==> {args}')
    # 使用with上下文管理器, 自动执行close
    async with __pool.acquire() as conn:
    # acquire: 从空闲池获得连接。如果需要,并且池的大小小于maxsize,则创建新连接。
    async with conn.cursor(aiomysql.DictCursor) as cur:
    # cursor: 连接的游标
    # DictCursor: 作为字典返回结果的游标
    await cur.execute(sql.replace('?', '%s'), args or ())
    # sql.replace('?', '%s'): 'SELECT * FROM users WHERE uid=?'.replace('?', '%s')
    # args or (): 'SELECT * FROM users WHERE uid=%s' % (101,)
    if size:
    rs = await cur.fetchmany(size)
    else:
    rs = await cur.fetchall()
    print(f'rows returned: {len(rs)}')
    return rs
    @staticmethod
    async def execute(sql, args, autocommit=True):
    '''
    INSERT、UPDATE、DELETE操作,可以通用的execute函数,
    因为这3种SQL的执行都需要相同的参数, 返回一个整数表示影响的行数
    '''
    print(f'{sql} ==> {args}')
    async with __pool.acquire() as conn:
    if not autocommit:
    await conn.begin() # 开始处理
    try:
    async with conn.cursor(aiomysql.DictCursor) as cur:
    await cur.execute(sql.replace('?', '%s'), args)
    affected = cur.rowcount # 受影响的行数
    if not autocommit:
    await conn.commit() # 提交更改, 非自动提交时才需要
    except Exception as e:
    if not autocommit:
    await conn.rollback() # 回滚更改
    raise Exception(e)
    return affected
    

测试下select

if __name__ == '__main__':
import asyncio
loop = asyncio.get_event_loop()
loop.run_until_complete(Mysql.createPool())
rs = loop.run_until_complete(Mysql.select('select uid, name from users where uid=?', [101]))
print(rs)
  • 控制台输出
创建成功
select * from users where uid=? ==> [101]
rows returned: 1
[{'uid': 101, 'name': 'z417'}]

总结

  1. 定义了Mysql类, 其中有3个静态方法

  2. 引入了异步, 调用方式共分两步

版权声明
本文为[z417]所创,转载请带上原文链接,感谢
https://www.cnblogs.com/z417/p/13993100.html

  1. 利用Python爬虫获取招聘网站职位信息
  2. Using Python crawler to obtain job information of recruitment website
  3. Several highly rated Python libraries arrow, jsonpath, psutil and tenacity are recommended
  4. Python装饰器
  5. Python实现LDAP认证
  6. Python decorator
  7. Implementing LDAP authentication with Python
  8. Vscode configures Python development environment!
  9. In Python, how dare you say you can't log module? ️
  10. 我收藏的有关Python的电子书和资料
  11. python 中 lambda的一些tips
  12. python中字典的一些tips
  13. python 用生成器生成斐波那契数列
  14. python脚本转pyc踩了个坑。。。
  15. My collection of e-books and materials about Python
  16. Some tips of lambda in Python
  17. Some tips of dictionary in Python
  18. Using Python generator to generate Fibonacci sequence
  19. The conversion of Python script to PyC stepped on a pit...
  20. Python游戏开发,pygame模块,Python实现扫雷小游戏
  21. Python game development, pyGame module, python implementation of minesweeping games
  22. Python实用工具,email模块,Python实现邮件远程控制自己电脑
  23. Python utility, email module, python realizes mail remote control of its own computer
  24. 毫无头绪的自学Python,你可能连门槛都摸不到!【最佳学习路线】
  25. Python读取二进制文件代码方法解析
  26. Python字典的实现原理
  27. Without a clue, you may not even touch the threshold【 Best learning route]
  28. Parsing method of Python reading binary file code
  29. Implementation principle of Python dictionary
  30. You must know the function of pandas to parse JSON data - JSON_ normalize()
  31. Python实用案例,私人定制,Python自动化生成爱豆专属2021日历
  32. Python practical case, private customization, python automatic generation of Adu exclusive 2021 calendar
  33. 《Python实例》震惊了,用Python这么简单实现了聊天系统的脏话,广告检测
  34. "Python instance" was shocked and realized the dirty words and advertisement detection of the chat system in Python
  35. Convolutional neural network processing sequence for Python deep learning
  36. Python data structure and algorithm (1) -- enum type enum
  37. 超全大厂算法岗百问百答(推荐系统/机器学习/深度学习/C++/Spark/python)
  38. 【Python进阶】你真的明白NumPy中的ndarray吗?
  39. All questions and answers for algorithm posts of super large factories (recommended system / machine learning / deep learning / C + + / spark / Python)
  40. [advanced Python] do you really understand ndarray in numpy?
  41. 【Python进阶】Python进阶专栏栏主自述:不忘初心,砥砺前行
  42. [advanced Python] Python advanced column main readme: never forget the original intention and forge ahead
  43. python垃圾回收和缓存管理
  44. java调用Python程序
  45. java调用Python程序
  46. Python常用函数有哪些?Python基础入门课程
  47. Python garbage collection and cache management
  48. Java calling Python program
  49. Java calling Python program
  50. What functions are commonly used in Python? Introduction to Python Basics
  51. Python basic knowledge
  52. Anaconda5.2 安装 Python 库(MySQLdb)的方法
  53. Python实现对脑电数据情绪分析
  54. Anaconda 5.2 method of installing Python Library (mysqldb)
  55. Python implements emotion analysis of EEG data
  56. Master some advanced usage of Python in 30 seconds, which makes others envy it
  57. python爬取百度图片并对图片做一系列处理
  58. Python crawls Baidu pictures and does a series of processing on them
  59. python链接mysql数据库
  60. Python link MySQL database