十六天编写一个博客应用程序（2）

1.数据表

该博客网站需创建3个表：users,blogs,comments。

users表，用来保存用户：

blogs表，用来保存博客：

comments表，用来保存评论：

DROP DATABASE IF EXISTS awesome_blogs;

CREATE DATABASE awesome_blogs;

USE awesome_blogs;

GRANT SELECT, INSERT, UPDATE, DELETE ON awesome_blogs.* TO 'www-data'@'localhost' IDENTIFIED BY 'www-data';

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;

UNIQUE KEY表示所有记录中该字段不能重复出现， PRIMARY KEY的为主键。

将其复制到sqlyog后点击执行，便自行创建各表：

2.在一个Web App中，所有数据，包括用户信息、发布的日志、评论等，都存储在数据库中。在awesome-python3-webapp中，我们选择MySQL作为数据库。Web App里面有很多地方都要访问数据库。访问数据库需要创建数据库连接、游标对象，然后执行SQL语句，最后处理异常，清理资源。这些访问数据库的代码如果分散到各个函数中，势必无法维护，也不利于代码复用。所以，我们要首先把常用的SELECT、INSERT、UPDATE和DELETE操作用函数封装起来。

由于Web框架使用了基于asyncio的aiohttp，这是基于协程的异步模型。在协程中，不能调用普通的同步IO操作，因为所有用户都是由一个线程服务的，协程的执行速度必须非常快，才能处理大量用户的请求。而耗时的IO操作不能在协程中以同步的方式调用，否则，等待一个IO操作时，系统无法响应任何其他用户。

这就是异步编程的一个原则：一旦决定使用异步，则系统每一层都必须是异步，“开弓没有回头箭”。

幸运的是aiomysql为MySQL数据库提供了异步IO的驱动。

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2.在www文件夹下面新建org.py

具体的可参照廖老师的网站

整个org.py为：

import asyncio, logging
import aiomysql
from PyQt5.QtCore.QProcess import StandardError


def log(sql, args = ()):
    logging.info('SQL:%s' % sql)

async def create_pool(loop, **kw):
    logging.info('create database connection pool...')
    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', 'utf-8'),
        autocommit=kw.get('autocommit', True),
        maxsize=kw.get('maxsize', 10),
        minsize=kw.get('minsize', 1),
        loop=loop
    )

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 ())
            if size:
                rs = await cur.fetchmany(size)
            else:
                rs = await cur.fetchall()
        logging.info('rows returned:%s' % len(rs))
        return rs

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

def create_args_string(num):
    L = []
    for n in range(num):
        L.append('?')
    return ', '.join(L)

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)

class StringField(Field):

    def __init__(self, name=None, primary_key=False, default=None, ddl='varchar(100)'):
        super().__init__(name, ddl, primary_key, default)

class BooleanField(Field):

    def __init__(self, name=None, default=False):
        super().__init__(name, 'boolean', False, default)

class IntegerField(Field):

    def __init__(self, name=None, primary_key=False, default=0):
        super().__init__(name, 'bigint', primary_key, default)

class FloatField(Field):

    def __init__(self, name=None, primary_key=False, default=0.0):
        super().__init__(name, 'real', primary_key, default)

class TextField(Field):

    def __init__(self, name=None, default=None):
        super().__init__(name, 'text', False, default)

class ModelMetaclass(type):

    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 StandardError('Duplicate primary key for field: %s' % k)
                    primaryKey = k
                else:
                    fields.append(k)
        if not primaryKey:
            raise StandardError('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
    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)

copy完上面的代码，我就在思考一个问题，以上这些要是脱了普我真的能完成吗？那我的目的到底是什么？我想，我本来就是想自己动手弄一个博客程序，但是我发现这没有几年的功力根本实现不了。so，我想到了一条邪路：我只需要在github上面把这个项目复制下来，再部署到我本地，然后再添加些我想要的功能（昨天我就写了一个自动刷阅读量的程序），不就行了？

所有，下一篇博客我的打算就是部署整个项目。