廖雪峰python实战day3、day4：ORM和Model部分学习笔记

看了好几天，大体上是看懂了。
以Model类里面的save()方法为例，各值的传递情况基本上如下：


廖老师的代码报错，做了一些小修改之后成功运行。
ORM.py ：

import asyncio, logging

import aiomysql

def log(sql, args=()):
    logging.info('SQL: %s' % sql)
#创建地址池，在建立连接的时候通过关键字参数**kw将'user'，'password'，'db'传入，如果不通过**kw参数指定，则'host','port'等参数将默认
async def create_pool(loop, **kw):
    logging.info('create database connection pool...')
    #连接池由全局变量__pool存储
    global __pool
    __pool = await aiomysql.create_pool(
        host=kw.get('host', 'localhost'),
        port=kw.get('port', 3306),
        user=kw['user'],
        password=kw['password'],
        db=kw['db'],
        charset=kw.get('charset', 'utf8'),
        autocommit=kw.get('autocommit', True),
        maxsize=kw.get('maxsize', 10),
        minsize=kw.get('minsize', 1),
        loop=loop
    )
#每个HTTP请求都可以从连接池中直接获取数据库连接。使用连接池的好处是不必频繁地打开和关闭数据库连接，而是能复用就尽量复用。

#要执行SELECT语句，我们用select函数执行，需要传入SQL语句和SQL参数。使用replace函数将传入的sql语句中的'?'替换为'%s'，而后使用args内的具体执行参数代入执行
#据说使用带参数的SQL，而不是自己拼接SQL字符串，可以防止SQL注入攻击
async def select(sql, args, size=None):
    log(sql, args)
    global __pool
    async with __pool.get() as conn:
        async with conn.cursor(aiomysql.DictCursor) as cur:
            await cur.execute(sql.replace('?', '%s'), args or ())
            #如果传入size参数，就通过fetchmany()获取最多指定数量的记录，否则，通过fetchall()获取所有记录。
            if size:
                rs = await cur.fetchmany(size)
            else:
                rs = await cur.fetchall()
        logging.info('rows returned: %s' % len(rs))
        return rs
#要执行INSERT、UPDATE、DELETE语句，可以定义一个通用的execute()函数，因为这3种SQL的执行都需要相同的参数
async def execute(sql, args, autocommit=True):
    log(sql)
    async with __pool.get() as conn:
        if not autocommit:
            await conn.begin()
        try:
            async with conn.cursor(aiomysql.DictCursor) as cur:
                await cur.execute(sql.replace('?','%s'),args)
                affected = cur.rowcount
            if not autocommit:
                await conn.commit()
        except BaseException as e:
            if not autocommit:
                await conn.rollback()
            raise
        return affected
#该函数的功能是将通过传入一个int,返回一个等同数量的使用逗号隔开的？的字符串。
def create_args_string(num):
    L = []
    for n in range(num):
        L.append('?')
    return ', '.join(L)

#定义Field类以及各种Field的子类，用来映射各种不同的数据类型。
#__init__中的参数primary_key，default,column_type等分别用来指定 该类实例化之后用来映射的数据表字段的 是否主键，默认值和类型。
class Field(object):

    def __init__(self, name, column_type, primary_key, default):
        self.name = name
        self.column_type = column_type
        self.primary_key = primary_key
        self.default = default

    def __str__(self):
        return '<%s, %s:%s>' % (self.__class__.__name__, self.column_type, self.name)
#映射String
class StringField(Field):

    def __init__(self, name=None, primary_key=False, default=None, ddl='varchar(100)'):
        super().__init__(name, ddl, primary_key, default)
#映射布尔类型
class BooleanField(Field):

    def __init__(self, name=None, default=False):
        super().__init__(name, 'boolean', False, default)
#映射int类型
class IntegerField(Field):

    def __init__(self, name=None, primary_key=False, default=0):
        super().__init__(name, 'bigint', primary_key, default)
#映射Float类型
class FloatField(Field):

    def __init__(self, name=None, primary_key=False, default=0.0):
        super().__init__(name, 'real', primary_key, default)
#映射文本类型
class TextField(Field):

    def __init__(self, name=None, default=None):
        super().__init__(name, 'text', False, default)
#构建元类
#关系数据库的一行映射为一个对象，也就是一个类对应一个表
#子类继承Model类并创建后（创建数据表），
#类所有的属性（也就是数据表各个字段的名字，类型，是否主键，默认值）被映射到元类并经过一系列的处理赋值给一些变量（mappings,primarykey,fields,tableName），随后删除这些属性。
#最后根据这些变量生成__mappings__、__fields__等供之后使用。
#也就是把子类的所有属性根据其特征处理，存储到自身的类属性如__table__,__mapping__中去。
#或者生成一些带参数的sql语句，也存储到自身的类属性比如__select__,__insert__中去
class ModelMetaclass(type):
#__new__()方法接收到的参数依次是：当前准备创建的类的对象；类的名字；类继承的父类集合；类的属性集合。
    def __new__(cls, name, bases, attrs):
        if name=='Model':
            return type.__new__(cls, name, bases, attrs)
        tableName = attrs.get('__table__', None) or name
        logging.info('found model: %s (table: %s)' % (name, tableName))
        mappings = dict()
        fields = []
        primaryKey = None
        for k, v in attrs.items():
            if isinstance(v, Field):
                logging.info('  found mapping: %s ==> %s' % (k, v))
                mappings[k] = v
                if v.primary_key:
                    # 找到主键:
                    if primaryKey:
                        raise Exception('Duplicate primary key for field: %s' % k)
                    primaryKey = k
                else:
                    fields.append(k)
        if not primaryKey:
            raise Exception('Primary key not found.')
        for k in mappings.keys():
            attrs.pop(k)
        escaped_fields = list(map(lambda f: '`%s`' % f, fields))
        attrs['__mappings__'] = mappings # 保存属性和列的映射关系
        attrs['__table__'] = tableName
        attrs['__primary_key__'] = primaryKey # 主键属性名
        attrs['__fields__'] = fields # 除主键外的属性名
        attrs['__select__'] = 'select `%s`, %s from `%s`' % (primaryKey, ', '.join(escaped_fields), tableName)
        attrs['__insert__'] = 'insert into `%s` (%s, `%s`) values (%s)' % (tableName, ', '.join(escaped_fields), primaryKey, create_args_string(len(escaped_fields) + 1))
        attrs['__update__'] = 'update `%s` set %s where `%s`=?' % (tableName, ', '.join(map(lambda f: '`%s`=?' % (mappings.get(f).name or f), fields)), primaryKey)
        attrs['__delete__'] = 'delete from `%s` where `%s`=?' % (tableName, primaryKey)
        return type.__new__(cls, name, bases, attrs)

class Model(dict, metaclass=ModelMetaclass):

    def __init__(self, **kw):
        super(Model, self).__init__(**kw)

    def __getattr__(self, key):
        try:
            return self[key]
        except KeyError:
            raise AttributeError(r"'Model' object has no attribute '%s'" % key)

    def __setattr__(self, key, value):
        self[key] = value

    def getValue(self, key):
        return getattr(self, key, None)

    def getValueOrDefault(self, key):
        value = getattr(self, key, None)
        if value is None:
            field = self.__mappings__[key]
            if field.default is not None:
                value = field.default() if callable(field.default) else field.default
                logging.debug('using default value for %s: %s' % (key, str(value)))
                setattr(self, key, value)
        return value
 	#classmethod 修饰符对应的函数不需要实例化，不需要 self 参数，
    # 但第一个参数需要是表示自身类的 cls 参数，
    # 可以来调用类的属性，类的方法，实例化对象等。
    #并且有子类继承时，调用该类方法时，传入的类变量cls的是子类，而非父类。
    @classmethod
    async def findAll(cls, where=None, args=None, **kw):
        ' find objects by where clause. '
        sql = [cls.__select__]
        if where:
            sql.append('where')
            sql.append(where)
        if args is None:
            args = []
        orderBy = kw.get('orderBy', None)
        if orderBy:
            sql.append('order by')
            sql.append(orderBy)
        limit = kw.get('limit', None)
        if limit is not None:
            sql.append('limit')
            if isinstance(limit, int):
                sql.append('?')
                args.append(limit)
            elif isinstance(limit, tuple) and len(limit) == 2:
                sql.append('?, ?')
                args.extend(limit)
            else:
                raise ValueError('Invalid limit value: %s' % str(limit))
        rs = await select(' '.join(sql), args)
        return [cls(**r) for r in rs]

    @classmethod
    async def findNumber(cls, selectField, where=None, args=None):
        ' find number by select and where. '
        sql = ['select %s _num_ from `%s`' % (selectField, cls.__table__)]
        if where:
            sql.append('where')
            sql.append(where)
        rs = await select(' '.join(sql), args, 1)
        if len(rs) == 0:
            return None
        return rs[0]['_num_']

    @classmethod
    async def find(cls, pk):
        ' find object by primary key. '
        rs = await select('%s where `%s`=?' % (cls.__select__, cls.__primary_key__), [pk], 1)
        if len(rs) == 0:
            return None
        return cls(**rs[0])

    async def save(self):
        args = list(map(self.getValueOrDefault, self.__fields__))
        args.append(self.getValueOrDefault(self.__primary_key__))
        rows = await execute(self.__insert__,args)
        if rows != 1:
            logging.warn('failed to insert record: affected rows: %s' % rows)

    async def update(self):
        args = list(map(self.getValue, self.__fields__))
        args.append(self.getValue(self.__primary_key__))
        rows = await execute(self.__update__, args)
        if rows != 1:
            logging.warn('failed to update by primary key: affected rows: %s' % rows)

    async def remove(self):
        args = [self.getValue(self.__primary_key__)]
        rows = await execute(self.__delete__, args)
        if rows != 1:
            logging.warn('failed to remove by primary key: affected rows: %s' % rows)

models.py :

import time, uuid

from ORM import Model, StringField, BooleanField, FloatField, TextField

def next_id():
    return '%015d%s000' % (int(time.time() * 1000), uuid.uuid4().hex)

class User(Model):
    __table__ = 'users'

    id = StringField(primary_key=True, default=next_id, ddl='varchar(50)')
    email = StringField(ddl='varchar(50)')
    passwd = StringField(ddl='varchar(50)')
    admin = BooleanField()
    name = StringField(ddl='varchar(50)')
    image = StringField(ddl='varchar(500)')
    created_at = FloatField(default=time.time)

class Blog(Model):
    __table__ = 'blogs'

    id = StringField(primary_key=True, default=next_id, ddl='varchar(50)')
    user_id = StringField(ddl='varchar(50)')
    user_name = StringField(ddl='varchar(50)')
    user_image = StringField(ddl='varchar(500)')
    name = StringField(ddl='varchar(50)')
    summary = StringField(ddl='varchar(200)')
    content = TextField()
    created_at = FloatField(default=time.time)

class Comment(Model):
    __table__ = 'comments'

    id = StringField(primary_key=True, default=next_id, ddl='varchar(50)')
    blog_id = StringField(ddl='varchar(50)')
    user_id = StringField(ddl='varchar(50)')
    user_name = StringField(ddl='varchar(50)')
    user_image = StringField(ddl='varchar(500)')
    content = TextField()
    created_at = FloatField(default=time.time)

创建sql脚本文件：

-- schema.sql

drop database if exists awesome;

create database awesome;

use awesome;
--这里要特别注意，先create，再alter，最后再grant，至于为什么我也不知道。。。
create user 'www-data'@'localhost' identified by 'www-data';
alter user 'www-data'@'localhost' identified with mysql_native_password by 'www-data';
grant select, insert, update, delete on awesome.* to 'www-data'@'localhost';

create table users (
    `id` varchar(50) not null,
    `email` varchar(50) not null,
    `passwd` varchar(50) not null,
    `admin` bool not null,
    `name` varchar(50) not null,
    `image` varchar(500) not null,
    `created_at` real not null,
    unique key `idx_email` (`email`),
    key `idx_created_at` (`created_at`),
    primary key (`id`)
) engine=innodb default charset=utf8;

create table blogs (
    `id` varchar(50) not null,
    `user_id` varchar(50) not null,
    `user_name` varchar(50) not null,
    `user_image` varchar(500) not null,
    `name` varchar(50) not null,
    `summary` varchar(200) not null,
    `content` mediumtext not null,
    `created_at` real not null,
    key `idx_created_at` (`created_at`),
    primary key (`id`)
) engine=innodb default charset=utf8;

create table comments (
    `id` varchar(50) not null,
    `blog_id` varchar(50) not null,
    `user_id` varchar(50) not null,
    `user_name` varchar(50) not null,
    `user_image` varchar(500) not null,
    `content` mediumtext not null,
    `created_at` real not null,
    key `idx_created_at` (`created_at`),
    primary key (`id`)
) engine=innodb default charset=utf8;

创建完毕使用命令行mysql -u root -p < 路径\schema.sql运行该sql脚本。

测试文件test.py :

import ORM
import asyncio
from models import User, Blog, Comment

async def test(loop):
    await ORM.create_pool(loop=loop, user='root', password='12345', db='awesome')
    u = User(name='Test', email='[email protected]', passwd='1234567890', image='about:blank')
    await u.save()
    #这里要close,至于为什么，我还是不知道。。。
    ORM.__pool.close()
    await ORM.__pool.wait_closed()
if __name__ == '__main__':
    loop = asyncio.get_event_loop()
    loop.run_until_complete(test(loop))
    loop.close()

执行完毕使用命令行mysql -u root -p， use awesome; ，select * from users;检查数据是否被插入。