#!/usr/bin/env python
# -*- coding: utf-8 -*-"""
设计db模块的原因：1. 更简单的操作数据库一次数据访问：   数据库连接 => 游标对象 => 执行SQL => 处理异常 => 清理资源。db模块对这些过程进行封装，使得用户仅需关注SQL执行。2. 数据安全用户请求以多线程处理时，为了避免多线程下的数据共享引起的数据混乱，需要将数据连接以ThreadLocal对象传入。
设计db接口：1.设计原则：根据上层调用者设计简单易用的API接口2. 调用接口1. 初始化数据库连接信息create_engine封装了如下功能:1. 为数据库连接 准备需要的配置信息2. 创建数据库连接(由生成的全局对象engine的 connect方法提供)from transwarp import dbdb.create_engine(user='root',password='password',database='test',host='127.0.0.1',port=3306)2. 执行SQL DMLselect 函数封装了如下功能:1.支持一个数据库连接里执行多个SQL语句2.支持链接的自动获取和释放使用样例:users = db.select('select * from user')# users =># [#     { "id": 1, "name": "Michael"},#     { "id": 2, "name": "Bob"},#     { "id": 3, "name": "Adam"}# ]3. 支持事物transaction 函数封装了如下功能:1. 事务也可以嵌套，内层事务会自动合并到外层事务中，这种事务模型足够满足99%的需求
"""import time
import uuid
import functools
import threading
import logging# global engine object:
engine = Nonedef next_id(t=None):"""生成一个唯一id   由 当前时间 + 随机数（由伪随机数得来）拼接得到"""if t is None:t = time.time()return '%015d%s000' % (int(t * 1000), uuid.uuid4().hex)def _profiling(start, sql=''):"""用于剖析sql的执行时间"""t = time.time() - startif t > 0.1:logging.warning('[PROFILING] [DB] %s: %s' % (t, sql))else:logging.info('[PROFILING] [DB] %s: %s' % (t, sql))def create_engine(user, password, database, host='127.0.0.1', port=3306, **kw):"""db模型的核心函数，用于连接数据库, 生成全局对象engine，engine对象持有数据库连接"""import mysql.connectorglobal engineif engine is not None:raise DBError('Engine is already initialized.')params = dict(user=user, password=password, database=database, host=host, port=port)defaults = dict(use_unicode=True, charset='utf8', collation='utf8_general_ci', autocommit=False)for k, v in defaults.iteritems():params[k] = kw.pop(k, v)params.update(kw)params['buffered'] = Trueengine = _Engine(lambda: mysql.connector.connect(**params))# test connection...logging.info('Init mysql engine <%s> ok.' % hex(id(engine)))def connection():"""db模块核心函数，用于获取一个数据库连接通过_ConnectionCtx对 _db_ctx封装，使得惰性连接可以自动获取和释放，也就是可以使用 with语法来处理数据库连接_ConnectionCtx    实现with语法^|_db_ctx           _DbCtx实例^|_DbCtx            获取和释放惰性连接^|_LasyConnection   实现惰性连接"""return _ConnectionCtx()def with_connection(func):"""设计一个装饰器 替换with语法，让代码更优雅比如:@with_connectiondef foo(*args, **kw):f1()f2()f3()"""@functools.wraps(func)def _wrapper(*args, **kw):with _ConnectionCtx():return func(*args, **kw)return _wrapperdef transaction():"""db模块核心函数 用于实现事物功能支持事物:with db.transaction():db.select('...')db.update('...')db.update('...')支持事物嵌套:with db.transaction():transaction1transaction2..."""return _TransactionCtx()def with_transaction(func):"""设计一个装饰器 替换with语法，让代码更优雅比如:@with_transactiondef do_in_transaction():>>> @with_transaction... def update_profile(id, name, rollback):...     u = dict(id=id, name=name, email='%s@test.org' % name, passwd=name, last_modified=time.time())...     insert('user', **u)...     update('update user set passwd=? where id=?', name.upper(), id)...     if rollback:...         raise StandardError('will cause rollback...')>>> update_profile(8080, 'Julia', False)>>> select_one('select * from user where id=?', 8080).passwdu'JULIA'>>> update_profile(9090, 'Robert', True)Traceback (most recent call last):...StandardError: will cause rollback..."""@functools.wraps(func)def _wrapper(*args, **kw):start = time.time()with _TransactionCtx():func(*args, **kw)_profiling(start)return _wrapper@with_connection
def _select(sql, first, *args):"""执行SQL，返回一个结果 或者多个结果组成的列表"""global _db_ctxcursor = Nonesql = sql.replace('?', '%s')logging.info('SQL: %s, ARGS: %s' % (sql, args))try:cursor = _db_ctx.connection.cursor()cursor.execute(sql, args)if cursor.description:names = [x[0] for x in cursor.description]if first:values = cursor.fetchone()if not values:return Nonereturn Dict(names, values)return [Dict(names, x) for x in cursor.fetchall()]finally:if cursor:cursor.close()def select_one(sql, *args):"""执行SQL 仅返回一个结果如果没有结果 返回None如果有1个结果，返回一个结果如果有多个结果，返回第一个结果>>> u1 = dict(id=100, name='Alice', email='alice@test.org', passwd='ABC-12345', last_modified=time.time())>>> u2 = dict(id=101, name='Sarah', email='sarah@test.org', passwd='ABC-12345', last_modified=time.time())>>> insert('user', **u1)1>>> insert('user', **u2)1>>> u = select_one('select * from user where id=?', 100)>>> u.nameu'Alice'>>> select_one('select * from user where email=?', 'abc@email.com')>>> u2 = select_one('select * from user where passwd=? order by email', 'ABC-12345')>>> u2.nameu'Alice'"""return _select(sql, True, *args)def select_int(sql, *args):"""执行一个sql 返回一个数值，注意仅一个数值，如果返回多个数值将触发异常>>> u1 = dict(id=96900, name='Ada', email='ada@test.org', passwd='A-12345', last_modified=time.time())>>> u2 = dict(id=96901, name='Adam', email='adam@test.org', passwd='A-12345', last_modified=time.time())>>> insert('user', **u1)1>>> insert('user', **u2)1>>> select_int('select count(*) from user')5>>> select_int('select count(*) from user where email=?', 'ada@test.org')1>>> select_int('select count(*) from user where email=?', 'notexist@test.org')0>>> select_int('select id from user where email=?', 'ada@test.org')96900>>> select_int('select id, name from user where email=?', 'ada@test.org')Traceback (most recent call last):...MultiColumnsError: Expect only one column."""d = _select(sql, True, *args)if len(d) != 1:raise MultiColumnsError('Expect only one column.')return d.values()[0]def select(sql, *args):"""执行sql 以列表形式返回结果>>> u1 = dict(id=200, name='Wall.E', email='wall.e@test.org', passwd='back-to-earth', last_modified=time.time())>>> u2 = dict(id=201, name='Eva', email='eva@test.org', passwd='back-to-earth', last_modified=time.time())>>> insert('user', **u1)1>>> insert('user', **u2)1>>> L = select('select * from user where id=?', 900900900)>>> L[]>>> L = select('select * from user where id=?', 200)>>> L[0].emailu'wall.e@test.org'>>> L = select('select * from user where passwd=? order by id desc', 'back-to-earth')>>> L[0].nameu'Eva'>>> L[1].nameu'Wall.E'"""return _select(sql, False, *args)@with_connection
def _update(sql, *args):"""执行update 语句，返回update的行数"""global _db_ctxcursor = Nonesql = sql.replace('?', '%s')logging.info('SQL: %s, ARGS: %s' % (sql, args))try:cursor = _db_ctx.connection.cursor()cursor.execute(sql, args)r = cursor.rowcountif _db_ctx.transactions == 0:# no transaction enviroment:logging.info('auto commit')_db_ctx.connection.commit()return rfinally:if cursor:cursor.close()def update(sql, *args):"""执行update 语句，返回update的行数>>> u1 = dict(id=1000, name='Michael', email='michael@test.org', passwd='123456', last_modified=time.time())>>> insert('user', **u1)1>>> u2 = select_one('select * from user where id=?', 1000)>>> u2.emailu'michael@test.org'>>> u2.passwdu'123456'>>> update('update user set email=?, passwd=? where id=?', 'michael@example.org', '654321', 1000)1>>> u3 = select_one('select * from user where id=?', 1000)>>> u3.emailu'michael@example.org'>>> u3.passwdu'654321'>>> update('update user set passwd=? where id=?', '***', '123')0"""return _update(sql, *args)def insert(table, **kw):"""执行insert语句>>> u1 = dict(id=2000, name='Bob', email='bob@test.org', passwd='bobobob', last_modified=time.time())>>> insert('user', **u1)1>>> u2 = select_one('select * from user where id=?', 2000)>>> u2.nameu'Bob'>>> insert('user', **u2)Traceback (most recent call last):...IntegrityError: 1062 (23000): Duplicate entry '2000' for key 'PRIMARY'"""cols, args = zip(*kw.iteritems())sql = 'insert into `%s` (%s) values (%s)' % (table, ','.join(['`%s`' % col for col in cols]), ','.join(['?' for i in range(len(cols))]))return _update(sql, *args)class Dict(dict):"""字典对象实现一个简单的可以通过属性访问的字典，比如 x.key = value"""def __init__(self, names=(), values=(), **kw):super(Dict, self).__init__(**kw)for k, v in zip(names, values):self[k] = vdef __getattr__(self, key):try:return self[key]except KeyError:raise AttributeError(r"'Dict' object has no attribute '%s'" % key)def __setattr__(self, key, value):self[key] = valueclass DBError(Exception):passclass MultiColumnsError(DBError):passclass _Engine(object):"""数据库引擎对象用于保存 db模块的核心函数：create_engine 创建出来的数据库连接"""def __init__(self, connect):self._connect = connectdef connect(self):return self._connect()class _LasyConnection(object):"""惰性连接对象仅当需要cursor对象时，才连接数据库，获取连接"""def __init__(self):self.connection = Nonedef cursor(self):if self.connection is None:_connection = engine.connect()logging.info('[CONNECTION] [OPEN] connection <%s>...' % hex(id(_connection)))self.connection = _connectionreturn self.connection.cursor()def commit(self):self.connection.commit()def rollback(self):self.connection.rollback()def cleanup(self):if self.connection:_connection = self.connectionself.connection = Nonelogging.info('[CONNECTION] [CLOSE] connection <%s>...' % hex(id(connection)))_connection.close()class _DbCtx(threading.local):"""db模块的核心对象, 数据库连接的上下文对象，负责从数据库获取和释放连接取得的连接是惰性连接对象，因此只有调用cursor对象时，才会真正获取数据库连接该对象是一个 Thread local对象，因此绑定在此对象上的数据 仅对本线程可见"""def __init__(self):self.connection = Noneself.transactions = 0def is_init(self):"""返回一个布尔值，用于判断 此对象的初始化状态"""return self.connection is not Nonedef init(self):"""初始化连接的上下文对象，获得一个惰性连接对象"""logging.info('open lazy connection...')self.connection = _LasyConnection()self.transactions = 0def cleanup(self):"""清理连接对象，关闭连接"""self.connection.cleanup()self.connection = Nonedef cursor(self):"""获取cursor对象， 真正取得数据库连接"""return self.connection.cursor()# thread-local db context:
_db_ctx = _DbCtx()class _ConnectionCtx(object):"""因为_DbCtx实现了连接的 获取和释放，但是并没有实现连接的自动获取和释放，_ConnectCtx在 _DbCtx基础上实现了该功能，因此可以对 _ConnectCtx 使用with 语法，比如：with connection():passwith connection():pass"""def __enter__(self):"""获取一个惰性连接对象"""global _db_ctxself.should_cleanup = Falseif not _db_ctx.is_init():_db_ctx.init()self.should_cleanup = Truereturn selfdef __exit__(self, exctype, excvalue, traceback):"""释放连接"""global _db_ctxif self.should_cleanup:_db_ctx.cleanup()class _TransactionCtx(object):"""事务嵌套比Connection嵌套复杂一点，因为事务嵌套需要计数，每遇到一层嵌套就+1，离开一层嵌套就-1，最后到0时提交事务"""def __enter__(self):global _db_ctxself.should_close_conn = Falseif not _db_ctx.is_init():# needs open a connection first:_db_ctx.init()self.should_close_conn = True_db_ctx.transactions += 1logging.info('begin transaction...' if _db_ctx.transactions == 1 else 'join current transaction...')return selfdef __exit__(self, exctype, excvalue, traceback):global _db_ctx_db_ctx.transactions -= 1try:if _db_ctx.transactions == 0:if exctype is None:self.commit()else:self.rollback()finally:if self.should_close_conn:_db_ctx.cleanup()def commit(self):global _db_ctxlogging.info('commit transaction...')try:_db_ctx.connection.commit()logging.info('commit ok.')except:logging.warning('commit failed. try rollback...')_db_ctx.connection.rollback()logging.warning('rollback ok.')raisedef rollback(self):global _db_ctxlogging.warning('rollback transaction...')_db_ctx.connection.rollback()logging.info('rollback ok.')if __name__ == '__main__':logging.basicConfig(level=logging.DEBUG)create_engine('www-data', 'www-data', 'test', '192.168.10.128')update('drop table if exists user')update('create table user (id int primary key, name text, email text, passwd text, last_modified real)')import doctestdoctest.testmod()