GAE Meets Django

使用Django创建
Google App Engine应用
林胜
linsheng.cn@gmail.com

• Google App Engine介绍
• Django介绍
• 代码示例

什么是Google App Engine
• Google的Web Hosting服务
• 将你的Web应用部署到Google的基础设施之上
• 使你的应用能自动Scaling和load balancing
• 提供数据存储服务
• 集成了Google User认证和Gmail等服务

运行环境和限制
• Python 2.5.2
• 内置Django 0.96.1，并支持所有支持CGI的框架
（以及任何使用CGI适配器的WSGI框架）
• 运行在Sandbox中，不能访问文件系统，不能建
立socket，不支持cron job，不能创建子进程
• 限定时间内必须返回response
• 应用必须是纯Python，不支持C的扩展

存储−Datastore
• 基于Google BigTable，分布式存储服务
• 面向对象，非系型数据库，不支持ORM
• 相同Model可以有不同的属性
• 支持查询，排序，事务
• 不支持join, sum, avg等，不支持存储过程
• 每次查询最多返回1000条记录
• 全文检索？

App Engine Service
• Google帐号认证
• Gmail（发送email）
• URL Fetch
• Memcached
• Image (PIL)

价格(免费部分)
Fixed Quota Per Day Usage Quotas
大约500万PV/月

价格（收费部分）
• $0.10 - $0.12 per CPU core-hour
• $0.15 - $0.18 per GB-month of storage
• $0.11 - $0.13 per GB outgoing bandwidth
• $0.09 - $0.11 per GB incoming bandwidth

申请Google App Engine
• http://appengine.google.com/
• 通过Gmail帐号
• 通过短信认证
• 域名: http://yourapp.appspot.com
• 可以通过Google Apps绑定自己的域名

用途
• 学习Web 发
• 尝试各 idea, 少startup的前期投入成本
• 解决scalability问题
• App Gallery http://appgallery.appspot.com/

未来计
• 对更多语言的支持
• 收费计
• 大数据量的上传和下载
• 离线处理
• 数据导入/导出

Django简介
• 一个基于Python的full-stack Web框架
• ORM, URL mapping, admin interface,
template, middleware, i18n, cache...
• 很快很强大

为什么用Django（而不是webapp）
• Google App Engine Helper for Django
• 功能更强大
• 可移植性

项目示例−Blog系统
项目名称 − OnlyPython

创建发环境
• 下载Google App Engine SDK
http://code.google.com/appengine/downloads.html
• 从SVN下载最新的Django源代码
http://code.djangoproject.com/svn/django/trunk/
• 下载Google App Engine Helper for Django
http://code.google.com/p/google-app-engine-django/

项目目录结构
--- appengine-django (app engine helper for django 源文件目录)
--- django (django源文件目录)
--- onlypy (项目代码目录)
--- static (静态文件目录，存放js, css, 图片等)
--- app.yaml (app engine配置文件)
--- index.yaml (app engine索引配置文件)
--- main.py (app engine的启动脚本)
--- manage.py (Django的管理脚本)
--- settings.py (项目配置文件)
--- urls.py (URL mapping)

app.yaml
application: onlypython
version: 1
runtime: python
api_version: 1
handlers:
‐ url: /static
static_dir: static
‐ url: /.*
  script: main.py

main.py
import os
import sys
import logging
from appengine_django import InstallAppengineHelperForDjango
InstallAppengineHelperForDjango()
# Google App Engine imports.
from google.appengine.ext.webapp import util
# Import the part of Django that we use here.
import django.core.handlers.wsgi
def main():
  # Create a Django application for WSGI.
  application = django.core.handlers.wsgi.WSGIHandler()
  # Run the WSGI CGI handler with that application.
  util.run_wsgi_app(application)
if __name__ == '__main__':
  main()

settings.py
TIME_ZONE = 'UTC'
MIDDLEWARE_CLASSES = (
    'django.middleware.common.CommonMiddleware',
    'appengine_django.auth.middleware.AuthenticationMiddleware',
)
ROOT_URLCONF = 'urls'
ROOT_PATH = os.path.dirname(__file__)
TEMPLATE_DIRS = (
    os.path.join(ROOT_PATH, 'onlypy/templates')
)
INSTALLED_APPS = (
     'appengine_django',
     'django.contrib.auth',
     'onlypy.blog',
   )

models.py
from google.appengine.ext import db 
class Category(db.Model):
    name = db.StringProperty()
    
    def __str__(self):
        return self.name
class Post(db.Model):
    author = db.UserProperty()
    title = db.StringProperty(required=True, verbose_name=u'标题')
    tag = db.StringProperty(verbose_name=u'标签')
    content = db.TextProperty(required=True, verbose_name=u'内容')
    create_time = db.DateTimeProperty(auto_now_add=True)
    update_time = db.DateTimeProperty(auto_now=True)
    category = db.ReferenceProperty(Category, required=True, verbose_name=u'类 ')
    is_published = db.BooleanProperty(verbose_name=u'已发布')
    
    def get_absolute_url(self) :
        return '/post/%s/'%self.key().id()

forms.py
from google.appengine.ext.db import djangoforms as forms
from models import Post
class PostForm(forms.ModelForm):
    class Meta:
        model = Post
        exclude = ['author']

views.py
def add_post(request):
    if request.method == 'GET':
        form = PostForm()
    
    if request.method == 'POST':
        form = PostForm(request.POST)
        if form.is_valid():
            post = form.save()
            post.author = users.get_current_user()
            post.put()
            return HttpResponseRedirect('/post/add/')
    return render_to_response('blog/add_post.html',
               {'form': form},
               context_instance=RequestContext(request))

add_post.html
{% extends "base.html" %}
{% block content %}
<h1>添加新文章</h1>
<form name="mainForm" method="post" action="">
    {{form.as_p}}
    <input type="submit" value="保存"/>
</form>
{% endblock %}

urls.py
from django.conf.urls.defaults import *
urlpatterns = patterns('onlypy.blog.views',
    (r'^post/add/$', 'add_post'),
)

Run
• cd /yourpath/onlypython/
• python ./manage.py runserver 127.0.0.1:8000

http://localhost:8000/post/add/

views.py
def list_post(request):
    posts = Post.all().order('‐create_time')
    if (not is_admin()):
        posts = posts.filter("is_published", True)
    
    return object_list(request, queryset=posts, allow_empty=True,
                template_name='blog/list_post.html', 
                extra_context={'is_admin': is_admin()},
                paginate_by=20)

index.yaml
indexes:
    ‐ kind: Post
      properties:
      ‐ name: is_published
      ‐ name: create_time
        direction: desc

list_post.html
{% extends "base.html" %}
{% load markup %}
{% load paginator %}
{% block content %}
{% for post in object_list %}
 
<table border="0" cellspacing="0" cellpadding="0" width="100%">
    <tr>
        <td valign="top">
            <h1 style="margin‐bottom: 2px;">
                <a href="/post/{{post.key.id}}">
                    [{{ post.category.name }}] {{ post.title }}{% if post.is_published %}
{%else%}(未发布){%endif%}
                </a>
            </h1>
            <p style="padding:0px; margin: 0px;" class="small_font">
                类 : <a href="/category/
{{ post.category.key.id }}/">{{ post.category.name }}</a> <span style="padding‐left: 
10px;">{{ post.author.nickname }}写于{{ post.create_time|date:"Y‐M‐d H:i" }}</span>
            </p>
        </td>
    </tr>
</table>
<div style="padding‐left: 30px;">
    {{ post.content|markdown }}
</div>
{% endfor %}
{% paginator %}
{% endblock %}

urls.py
from django.conf.urls.defaults import *
urlpatterns = patterns('onlypy.blog.views',
    (r'^post/add/$', 'add_post'),
    (r'^$', 'list_post'),
)

项目信息
• 项目代码 http://code.google.com/p/onlypy/
• 项目演示 http://www.onlypython.com

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