编写Python的web框架中的Model的教程

有了ORM，我们就可以把Web App需要的3个表用Model表示出来：

import time, uuidfrom transwarp.db import next_idfrom transwarp.orm import Model, StringField, BooleanField, FloatField, TextFieldclass User(Model):  __table__ = 'users'  id = StringField(primary_key=True, default=next_id, ddl='varchar(50)')  email = StringField(updatable=False, ddl='varchar(50)')  password = StringField(ddl='varchar(50)')  admin = BooleanField()  name = StringField(ddl='varchar(50)')  image = StringField(ddl='varchar(500)')  created_at = FloatField(updatable=False, default=time.time)class Blog(Model):  __table__ = 'blogs'  id = StringField(primary_key=True, default=next_id, ddl='varchar(50)')  user_id = StringField(updatable=False, 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(updatable=False, default=time.time)class Comment(Model):  __table__ = 'comments'  id = StringField(primary_key=True, default=next_id, ddl='varchar(50)')  blog_id = StringField(updatable=False, ddl='varchar(50)')  user_id = StringField(updatable=False, ddl='varchar(50)')  user_name = StringField(ddl='varchar(50)')  user_image = StringField(ddl='varchar(500)')  content = TextField()  created_at = FloatField(updatable=False, default=time.time)

在编写ORM时，给一个Field增加一个default参数可以让ORM自己填入缺省值，非常方便。并且，缺省值可以作为函数对象传入，在调用insert()时自动计算。

例如，主键id的缺省值是函数next_id，创建时间created_at的缺省值是函数time.time，可以自动设置当前日期和时间。

日期和时间用float类型存储在数据库中，而不是datetime类型，这么做的好处是不必关心数据库的时区以及时区转换问题，排序非常简单，显示的时候，只需要做一个float到str的转换，也非常容易。
初始化数据库表

如果表的数量很少，可以手写创建表的SQL脚本：

-- schema.sqldrop database if exists awesome;create database awesome;use awesome;grant select, insert, update, delete on awesome.* to 'www-data'@'localhost' identified by 'www-data';create table users (  `id` varchar(50) not null,  `email` varchar(50) not null,  `password` 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;