Google App Engine学习笔记

GoogleApp Engine

哈哈 Vista=Viruses+Intruders+Spyware+Trojans+Adware

Google App Engine and [b]Google Apps[/b]

Google App Engine

ā a platform for building and hosting web application on Google's infrastructure

āno servers to maintain: just upload application and it's ready to serve users

Google Apps

āgives everyone at your organization a custom email address.

ā tools for word processing spreadsheets and presentations

ā a shared calendaring system and acess to a flexible intranet system

ā Standalone security and compliance services

GAE Features

āDynamic web serving with full support for cmmon web technologies

āPersistent storage with queries,sorting and transactions(交易、交流、业务)

āAutomatic scaling and load balancing

āAPIs for authenticating(认证) users and sending email using Google Account

āA fully featured local development environment that simulates Google App Engine on developer's computer

The Data Store

āDistributed data storage service

āFeatures a query engine and supports transacions including optimistic(乐观、优化、开放式) locking and rollback

āThe distributed datastore grows with the data

āApp Engine datastore is not a traditonal relational database,queries are specified using a SQL-like query language called GQL

GAE Terms of Service-Partial

āMust provide legally adequate privacy notice and protection for those users.

āNothing in the Terms gives you a right to use any of Google's trade names,and other brand features.

GAE Application Environment

Sandbox:

āThe sandbox isolates your application in its own secure,reliable environment.

Python Runtime Environment:

āPython version 2.5.2 with the Python standard library

āPython APIs for the datastore,Google Accouts,URL fetch and email services.

āthe Django web application framework version 0.96.1

GAE Project

āA project requires at least one Python program and YAML file that tells the hosting web sever how to run and present your application in respoonse to user requests.

āYAML(YAML Ain't a Markup Language) is a cross-language. human-friendly. data-serialization language used for configuration files.persistence and

network messaging.

āYAML is easier to read by humans and consumes fewer runtime resources than XML

GAE Limitations

āAn application can only access other computers on the Internet through the provide URL fetch and email sevices and APIs.

āOther computers can only connect to the application by making HTTP(or HTTPS)requests on the standard ports.

āAn application cannot write to the file system.

āAn app can read files,but only files uploaded with the application code.

āThe app must use the App Engine data store for all data that persists between requests.
āApplication code only runs in response to a web request.

āMust return response data within a few seconds.

āA request handler cannot spawn a sub-process or execute code after the response has been sent.

Inline HTML vs Templates

āTemplates are used for separating the pressentation aspects of the application from its business logic.The template engine combines data provided by the application with one or more templates to produce a coherent view of the data.Use WSGI-compatible templating engines(e.g. Django template)int applications. The form handling and user output are quite simple.so using the mainForm() and a simple string replcace() call for the output is acceptable.

GData

āThe Google Data API(GData) provides a simple protocol for exchanging data between web applications over the RSS or Atom formats. GData is implemented through the Representational State Transfer(REST) protocol open to any application or device that can use HTTP1.1 and its basic API.

āGData provides a general model for feeds,queries and results.

āGAE applications can use the GData API for interacting with other Google properties such as these:

Authentication(认证)

Google Base

Calendar

Documents

Picasa Web Albums

YouTube

OO,relational DB,and Datastore

OBJECT ORIENTED	RELATIONAL DATABASE	DATASTORE
Class	Table	Kind
Object	Record	Entity
Attribute	Colum	Property

Query vs. GqlQuery

āThe Datastore API provides fine-grained(细致的) data manipulation(处理) through the Query and GqlQuery classes.

āThe Query class provides a Datastroe API for preparing queries based on application-defined entities.

āGqlQuery is the lowest-level querying API for the Datastore.It uses the App Engine GQL language, and it's limited to efficient data searches and retrieval operations(get() fetch() count() etc.)

Memcache API

āscenario(梗概):Multiple calls across multiple servers

āMemcache is a services that provides a key-value caching mechanism for efficient in-memory data retrieval(找回 检索 重获) across multiple instances of an GAE application. The Memcache API enables:

-A reduction in the number of Datastore queries.

-A reduction in the Datastore quota usage for popular pages.

-Caching of expensive query results.

-Implementation(工具 执行) of transient(短暂 暂时) counters

āUsing Mememcache for Session Data

-Since all sesion activity depends on the owner every usage of any persisted data results in a query.

-Executing queries on every page interaction is inefficient over the application lifetime.