Django 2.1.12 开发文档：从入门到精通

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"Django开发文档手册，英文版，详尽阐述了Django框架的各种功能和使用方法，包括模型层、视图层、模板层、表单处理、开发流程、管理后台、安全、国际化与本地化、性能优化、地理框架、Web应用工具和其他核心功能。教程覆盖了快速安装、编写第一个Django应用的7个部分以及如何编写可复用的应用教程。" Django是Python编程语言中的一款强大且流行的Web开发框架，它遵循“Don't Repeat Yourself”（DRY）原则，旨在提高开发效率，提供简洁明了的API和高度可定制性。这份文档手册是针对Django 2.1.12版本的，由Django Software Foundation发布，日期为2019年8月15日。文档首先介绍了获取帮助的途径和文档的组织结构，帮助新用户更好地理解和定位所需信息。接着，详细阐述了以下几个核心概念： 1. **模型层（Model Layer）**：Django中的模型是数据库的抽象，用于定义数据结构和业务逻辑。你可以在这里定义字段类型、关系和其他元数据，Django会自动生成SQL以操作数据库。 2. **视图层（View Layer）**：视图是应用程序的逻辑部分，负责接收HTTP请求，处理数据，并返回HTTP响应。它们通常与URL配置配合工作，根据不同的URL调用不同的视图函数或类。 3. **模板层（Template Layer）**：Django的模板系统允许开发者使用一种简单的标记语言来设计HTML页面，并能够动态插入Python表达式，实现数据的渲染。 4. **表单（Forms）**：Django提供了强大的表单处理机制，可以从模型或自定义类生成表单，处理用户输入，验证数据并将其保存到数据库。 5. **开发过程（Development Process）**：文档涵盖了如何设置开发环境，使用版本控制，以及调试和测试技巧。 6. **管理后台（Admin）**：Django内置的管理后台让开发者能够快速创建一个后台管理系统，方便对模型数据进行添加、修改和删除等操作。 7. **安全（Security）**：这部分内容强调了Django的安全特性，如防止XSS和CSRF攻击，以及如何正确处理用户输入以防止SQL注入。 8. **国际化与本地化（Internationalization and Localization）**：Django支持多语言应用，包括消息翻译和时间区域处理。 9. **性能优化（Performance and Optimization）**：这部分介绍了如何提高Django应用的运行效率，包括缓存策略、数据库优化和减少模板渲染时间。 10. **地理框架（Geographic Framework）**：Django提供了处理地理位置数据的能力，如GIS（地理信息系统）功能。 11. **常见Web应用工具（Common Web Application Tools）**：Django包含了许多用于处理常见Web开发任务的工具，如邮件发送、会话管理、中间件等。 12. **其他核心功能（Other Core Functionalities）**：除了上述特性，Django还提供了许多其他功能，如认证系统、中间件、URL路由等。此外，文档还包含了一个全面的入门教程，从快速安装指南开始，一步步指导用户编写并部署第一个Django应用，共分为7个部分。教程不仅适合初学者，也对有经验的开发者有价值，特别是关于如何编写可复用的应用的高级教程，有助于提升开发者的代码组织和模块化能力。最后，文档给出了下一步阅读的建议，帮助用户根据自己的需求和兴趣进一步深入学习Django的各个方面。整体来看，这份Django开发文档手册是开发者学习和参考的重要资源，无论是初学者还是经验丰富的开发者，都能从中受益。

Django Documentation, Release 2.1.12.dev20190815174031

Listing 3: mysite/news/admin.py

from django.contrib import admin

from . import models

admin.site.register(models.Article)

The philosophy here is that your site is edited by a staff, or a client, or maybe just you – and you don’t want to have to

deal with creating backend interfaces just to manage content.

One typical workﬂow in creating Django apps is to create models and get the admin sites up and running as fast as

possible, so your staff (or clients) can start populating data. Then, develop the way data is presented to the public.

2.1.5 Design your URLs

A clean, elegant URL scheme is an important detail in a high-quality Web application. Django encourages beautiful

URL design and doesn’t put any cruft in URLs, like .php or .asp.

To design URLs for an app, you create a Python module called a URLconf . A table of contents for your app, it contains

a simple mapping between URL patterns and Python callback functions. URLconfs also serve to decouple URLs from

Python code.

Here’s what a URLconf might look like for the Reporter/Article example above:

Listing 4: mysite/news/urls.py

from django.urls import path

from . import views

urlpatterns = [

path('articles/<int:year>/', views.year_archive),

path('articles/<int:year>/<int:month>/', views.month_archive),

path('articles/<int:year>/<int:month>/<int:pk>/', views.article_detail),

]

The code above maps URL paths to Python callback functions (“views”). The path strings use parameter tags to

“capture” values from the URLs. When a user requests a page, Django runs through each path, in order, and stops at

the ﬁrst one that matches the requested URL. (If none of them matches, Django calls a special-case 404 view.) This is

blazingly fast, because the paths are compiled into regular expressions at load time.

Once one of the URL patterns matches, Django calls the given view, which is a Python function. Each view gets

passed a request object – which contains request metadata – and the values captured in the pattern.

For example, if a user requested the URL “/articles/2005/05/39323/”, Django would call the function news.views.

article_detail(request, year=2005, month=5, pk=39323).

2.1.6 Write your views

Each view is responsible for doing one of two things: Returning an HttpResponse object containing the content

for the requested page, or raising an exception such as Http404. The rest is up to you.

Generally, a view retrieves data according to the parameters, loads a template and renders the template with the

retrieved data. Here’s an example view for year_archive from above:

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Django Documentation, Release 2.1.12.dev20190815174031

Listing 5: mysite/news/views.py

from django.shortcuts import render

from .models import Article

def year_archive(request, year):

a_list = Article.objects.filter(pub_date__year=year)

context = {'year': year, 'article_list': a_list}

return render(request, 'news/year_archive.html', context)

This example uses Django’s template system, which has several powerful features but strives to stay simple enough

for non-programmers to use.

2.1.7 Design your templates

The code above loads the news/year_archive.html template.

Django has a template search path, which allows you to minimize redundancy among templates. In your Django

settings, you specify a list of directories to check for templates with DIRS. If a template doesn’t exist in the ﬁrst

directory, it checks the second, and so on.

Let’s say the news/year_archive.html template was found. Here’s what that might look like:

Listing 6: mysite/news/templates/news/year_archive.html

{% extends "base.html" %}

{% block title %}Articles for {{ year }}{% endblock %}

{% block content %}

<h1>Articles for {{ year }}</h1>

{% for article in article_list %}

<p>{{ article.headline }}</p>

<p>By {{ article.reporter.full_name }}</p>

<p>Published {{ article.pub_date|date:"F j, Y" }}</p>

{% endfor %}

{% endblock %}

Variables are surrounded by double-curly braces. {{ article.headline }} means “Output the value of the

article’s headline attribute.” But dots aren’t used only for attribute lookup. They also can do dictionary-key lookup,

index lookup and function calls.

Note {{ article.pub_date|date:"F j, Y" }} uses a Unix-style “pipe” (the “|” character). This is called

a template ﬁlter, and it’s a way to ﬁlter the value of a variable. In this case, the date ﬁlter formats a Python datetime

object in the given format (as found in PHP’s date function).

You can chain together as many ﬁlters as you’d like. You can write custom template ﬁlters. You can write custom

template tags, which run custom Python code behind the scenes.

Finally, Django uses the concept of “template inheritance”. That’s what the {% extends "base.html" %}

does. It means “First load the template called ‘base’, which has deﬁned a bunch of blocks, and ﬁll the blocks with

the following blocks.” In short, that lets you dramatically cut down on redundancy in templates: each template has to

deﬁne only what’s unique to that template.

Here’s what the “base.html” template, including the use of static ﬁles, might look like:

2.1. Django at a glance 11

Django Documentation, Release 2.1.12.dev20190815174031

Listing 7: mysite/templates/base.html

{% load static %}

<html>

<head>

<title>{% block title %}{% endblock %}</title>

</head>

<body>

{% block content %}{% endblock %}

</body>

</html>

Simplistically, it deﬁnes the look-and-feel of the site (with the site’s logo), and provides “holes” for child templates to

ﬁll. This makes a site redesign as easy as changing a single ﬁle – the base template.

It also lets you create multiple versions of a site, with different base templates, while reusing child templates. Django’s

creators have used this technique to create strikingly different mobile versions of sites – simply by creating a new base

template.

Note that you don’t have to use Django’s template system if you prefer another system. While Django’s template

system is particularly well-integrated with Django’s model layer, nothing forces you to use it. For that matter, you

don’t have to use Django’s database API, either. You can use another database abstraction layer, you can read XML

ﬁles, you can read ﬁles off disk, or anything you want. Each piece of Django – models, views, templates – is decoupled

from the next.

2.1.8 This is just the surface

This has been only a quick overview of Django’s functionality. Some more useful features:

• A caching framework that integrates with memcached or other backends.

• A syndication framework that makes creating RSS and Atom feeds as easy as writing a small Python class.

• More sexy automatically-generated admin features – this overview barely scratched the surface.

The next obvious steps are for you to download Django, read the tutorial and join the community. Thanks for your

interest!

2.2 Quick install guide

Before you can use Django, you’ll need to get it installed. We have a complete installation guide that covers all

the possibilities; this guide will guide you to a simple, minimal installation that’ll work while you walk through the

introduction.

2.2.1 Install Python

Being a Python Web framework, Django requires Python. See What Python version can I use with Django? for details.

Python includes a lightweight database called SQLite so you won’t need to set up a database just yet.

Get the latest version of Python at https://www.python.org/downloads/ or with your operating system’s package man-

ager.

You can verify that Python is installed by typing python from your shell; you should see something like:

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• A public site that lets people view polls and vote in them.

• An admin site that lets you add, change, and delete polls.

We’ll assume you have Django installed already. You can tell Django is installed and which version by running the

following command in a shell prompt (indicated by the $ preﬁx):

$ python -m django --version

If Django is installed, you should see the version of your installation. If it isn’t, you’ll get an error telling “No module

named django”.

This tutorial is written for Django 2.1, which supports Python 3.5 and later. If the Django version doesn’t match, you

can refer to the tutorial for your version of Django by using the version switcher at the bottom right corner of this

page, or update Django to the newest version. If you’re using an older version of Python, check What Python version

can I use with Django? to ﬁnd a compatible version of Django.

See How to install Django for advice on how to remove older versions of Django and install a newer one.

Where to get help:

If you’re having trouble going through this tutorial, please post a message to django-users or drop by #django on

irc.freenode.net to chat with other Django users who might be able to help.

2.3.1 Creating a project

If this is your ﬁrst time using Django, you’ll have to take care of some initial setup. Namely, you’ll need to auto-

generate some code that establishes a Django project – a collection of settings for an instance of Django, including

database conﬁguration, Django-speciﬁc options and application-speciﬁc settings.

From the command line, cd into a directory where you’d like to store your code, then run the following command:

$ django-admin startproject mysite

This will create a mysite directory in your current directory. If it didn’t work, see Problems running django-admin.

Note: You’ll need to avoid naming projects after built-in Python or Django components. In particular, this means

you should avoid using names like django (which will conﬂict with Django itself) or test (which conﬂicts with a

built-in Python package).

Where should this code live?

If your background is in plain old PHP (with no use of modern frameworks), you’re probably used to putting code

under the Web server’s document root (in a place such as /var/www). With Django, you don’t do that. It’s not a

good idea to put any of this Python code within your Web server’s document root, because it risks the possibility that

people may be able to view your code over the Web. That’s not good for security.

Put your code in some directory outside of the document root, such as /home/mycode.

Let’s look at what startproject created:

14 Chapter 2. Getting started

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