Django Web开发入门基础

官方有很详细的文档，但是看过几遍之后如果要翻找还是有点麻烦，本文算作是学习笔记，提取一些关键点记录下来，另附上官方教程 编写你的第一个 Django 应用

注： 文中的指令使用py，是在Windows上，macOS要使用 python3

 1. 安装Django

Django 是一个基于 Python 的Web开发框架，安装前可以用下面的命令检查是否安装了 Django，如果已经安装，会显示版本，没有安装会提示没有该模块

py -m django --version

如果没有安装，可以使用下面的命令安装

py -m pip install Django

2. 创建项目

项目就是一个 project，一个项目可以包含多个 app，也可以理解为多个模块，创建项目使用如下命令，其中 mysite 是项目名称：

django-admin startproject mysite

在令窗口中，切到刚刚创建的项目的根目录（有 manage.py），在项目中创建一个app，名字就叫 polls

py manage.py startapp polls

 然后修改几个文件

polls/views.py

from django.http import HttpResponsedef index(request):return HttpResponse("Hello World!")

polls/urls.py

from django.urls import path
from . import viewsurlpatterns = [path("", views.index, name="index"),
]

mysite/urls.py

from django.contrib import admin
from django.urls import include, pathurlpatterns = [path("polls/", include("polls.urls")),path("admin/", admin.site.urls),
]

 最后启动服务，浏览器访问 http://localhost:8000/polls/

py manage.py runserver

3. 配置语言和时区 

项目配置在 mysite/settings.py

语言标识可以在这里查找 Language Identifiers (RFC 3066)

# 语言设置为中文
LANGUAGE_CODE = 'zh-Hans'

时区标识可以在这里查找 List of tz database time zones 

# 时区设置为北京时间
TIME_ZONE = 'Asia/Shanghai'

4. 数据库

就使用自带的 SQLite 吧，方便又简单，如果开发商用的Web App，建议使用其他数据库，要进行额外的配置。

（1）创建数据模型

修改 polls/models.py

import datetimefrom django.db import models
from django.utils import timezoneclass Question(models.Model):question_text = models.CharField(max_length=200)pub_date = models.DateTimeField("date published")def __str__(self):return self.question_textdef was_published_recently(self):return self.pub_date >= timezone.now() - datetime.timedelta(days=1)class Choice(models.Model):# Choice属于一个Questionquestion = models.ForeignKey(Question, on_delete=models.CASCADE)choice_text = models.CharField(max_length=200)votes = models.IntegerField(default=0)def __str__(self):return self.choice_text

（2）激活模型

修改 mysite/settings.py，在 INSTALLED_APP 中添加 polls.apps.PollsConfig

INSTALLED_APPS = ["polls.apps.PollsConfig","django.contrib.admin","django.contrib.auth","django.contrib.contenttypes","django.contrib.sessions","django.contrib.messages","django.contrib.staticfiles",
]

（3）创建数据迁移(尚未提交)

py manage.py makemigrations polls

查看创建的迁移使用的SQL语句，下面命令中的 0001 是上面创建迁移时生成的 polls/migrations/0001_initial.py 文件名中的数字

py manage.py sqlmigrate polls 0001

（4）提交迁移

py manage.py migrate

总结起来就三步：修改模型 -> 创建迁移 -> 提交迁移

 （5）玩转数据库API

打开交互式窗口

py manage.py shell

>>> from polls.models import Choice, Question
>>> Question.objects.all()
<QuerySet []>
>>> from django.utils import timezone
>>> q = Question(question_text="What's new?", pub_date=timezone.now())
>>> q.save()
>>> q.id
1
>>> q.question_text
"What's new?"
>>> q.pub_date
datetime.datetime(2012, 2, 26, 13, 0, 0, 775217, tzinfo=datetime.timezone.utc)
>>> q.question_text = "What's up?"
>>> q.save()
>>> Question.objects.all()
<QuerySet [<Question: Question object (1)>]>

>>> from polls.models import Choice, Question
>>> Question.objects.all()
<QuerySet [<Question: What's up?>]>
>>> Question.objects.filter(id=1)
<QuerySet [<Question: What's up?>]>
>>> Question.objects.filter(question_text__startswith="What")
<QuerySet [<Question: What's up?>]>
>>> from django.utils import timezone
>>> current_year = timezone.now().year
>>> Question.objects.get(pub_date__year=current_year)
<Question: What's up?>
>>> Question.objects.get(id=2)
Traceback (most recent call last):...
DoesNotExist: Question matching query does not exist.
>>> Question.objects.get(pk=1)
<Question: What's up?>
>>> q = Question.objects.get(pk=1)
>>> q.was_published_recently()
True
>>> q = Question.objects.get(pk=1)
>>> q.choice_set.all()
<QuerySet []>
>>> q.choice_set.create(choice_text="Not much", votes=0)
<Choice: Not much>
>>> q.choice_set.create(choice_text="The sky", votes=0)
<Choice: The sky>
>>> c = q.choice_set.create(choice_text="Just hacking again", votes=0)
>>> c.question
<Question: What's up?>>>> q.choice_set.all()
<QuerySet [<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]>
>>> q.choice_set.count()
3
>>> Choice.objects.filter(question__pub_date__year=current_year)
<QuerySet [<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]>
>>> c = q.choice_set.filter(choice_text__startswith="Just hacking")
>>> c.delete()

5. 创建管理员

 输入下面的命令，然后根据提示设置账户名，邮箱，密码

py manage.py createsuperuser

启动服务，浏览器访问 http://127.0.0.1:8000/admin/

py manage.py runserver

修改 polls/admin.py 让管理员可管理数据

from django.contrib import adminfrom .models import Questionadmin.site.register(Question)

管理员登录后

6. 使用 html 模板

（1）创建 HTML 文件

在 polls/ 目录下新建一个 templates 文件夹，在 polls\templates\ 目录下新建一个 polls 文件见，如果新建一个 HTML 文件，比如 index.html，其最终的路径为 mysite\polls\templates\polls\index.html，代码中将使用 polls\index.html

polls\templates\polls\index.html

{% if latest_question_list %}<ul>{% for question in latest_question_list %}<li><a href="{% url 'index' question.id %}">{{ question.question_text }}</a></li>{% endfor %}</ul>
{% else %}<p>No polls are available.</p>
{% endif %}

 polls\templates\polls\detail.html

<h1>{{ question.question_text }}</h1>
<ul>
{% for choice in question.choice_set.all %}<li>{{ choice.choice_text }}</li>
{% endfor %}
</ul>

（2）配置 view

修改 polls/views.py

from django.http import HttpResponse
from django.shortcuts import render, get_object_or_404from .models import Questiondef index(request):latest_question_list = Question.objects.order_by("-pub_date")[:5]context = {"latest_question_list": latest_question_list}return render(request, "polls/index.html", context)def detail(request, question_id):question = get_object_or_404(Question, pk=question_id)context = {"question": question}return render(request, "polls/detail.html", context)def results(request, question_id):return HttpResponse("Results")def vote(request, question_id):return HttpResponse("Vote")

（3）配置 url

修改 polls/urls.py

from django.urls import pathfrom . import viewsurlpatterns = [# ex: /polls/path("", views.index, name="index"),# ex: /polls/5/path("<int:question_id>/", views.detail, name="detail"),# ex: /polls/5/results/path("<int:question_id>/results/", views.results, name="results"),# ex: /polls/5/vote/path("<int:question_id>/vote/", views.vote, name="vote"),
]

（4）URL命名空间

当项目存在多个应用时，可能需要借助命名空间来确定url，在应用的 urls.py 中配置 app_name

from django.urls import pathfrom . import viewsapp_name = "polls"
urlpatterns = [# ex: /polls/path("", views.index, name="index"),# ex: /polls/5/path("<int:question_id>/", views.detail, name="detail"),# ex: /polls/5/results/path("<int:question_id>/results/", views.results, name="results"),# ex: /polls/5/vote/path("<int:question_id>/vote/", views.vote, name="vote"),
]

index.html 中添加 app_name:

{% if latest_question_list %}<ul>{% for question in latest_question_list %}<li><a href="{% url 'polls:index' question.id %}">{{ question.question_text }}</a></li>{% endfor %}</ul>
{% else %}<p>No polls are available.</p>
{% endif %}

（5）创建表单

 修改 detail.html

<form action="{% url 'polls:vote' question.id %}" method="post">
{% csrf_token %}
<fieldset><legend><h1>{{ question.question_text }}</h1></legend>{% if error_message %}<p><strong>{{ error_message }}</strong></p>{% endif %}{% for choice in question.choice_set.all %}<input type="radio" name="choice" id="choice{{ forloop.counter }}" value="{{ choice.id }}"><label for="choice{{ forloop.counter }}">{{ choice.choice_text }}</label><br>{% endfor %}
</fieldset>
<input type="submit" value="Vote">
</form>

表单中涉及投票页面和投票结果页面，得新增一个 results.html，并修改 views.py

results.html

<h1>{{ question.question_text }}</h1><ul>
{% for choice in question.choice_set.all %}<li>{{ choice.choice_text }} -- {{ choice.votes }} vote{{ choice.votes|pluralize }}</li>
{% endfor %}
</ul><a href="{% url 'polls:detail' question.id %}">Vote again?</a>

views.py 中修改 results 和 vote 方法

from django.http import HttpResponse, HttpResponseRedirect
from django.shortcuts import render, get_object_or_404
from django.urls import reversefrom .models import Question, Choicedef index(request):latest_question_list = Question.objects.order_by("-pub_date")[:5]context = {"latest_question_list": latest_question_list}return render(request, "polls/index.html", context)def detail(request, question_id):question = get_object_or_404(Question, pk=question_id)context = {"question": question}return render(request, "polls/detail.html", context)def results(request, question_id):question = get_object_or_404(Question, pk=question_id)return render(request, "polls/results.html", {"question": question})def vote(request, question_id):question = get_object_or_404(Question, pk=question_id)try:selected_choice = question.choice_set.get(pk=request.POST["choice"])except (KeyError, Choice.DoesNotExist):return render(request, "polls/detail.html",{"question": question,"error_message": "You didn't select a choice."},)else:selected_choice.votes += 1selected_choice.save()return HttpResponseRedirect(reverse("polls:results", args=(question.id,)))

7. 编写测试用例 

首先得有个bug，巧了，我们的 polls 应用现在就有一个小 bug 需要被修复：我们的要求是如果 Question 是在一天之内发布的， Question.was_published_recently() 方法将会返回 True ，然而现在这个方法在 Question 的 pub_date 字段比当前时间还晚时也会返回 True（这是个 Bug）。

 在 polls\tests.py 中编写测试代码

import datetimefrom django.test import TestCase
from django.utils import timezone
from .models import Questionclass QuestionModelTests(TestCase):def test_was_published_recently_with_future_question(self):"""检测异常：发布时间比当前时间还要晚"""time = timezone.now() + datetime.timedelta(days=30)future_question = Question(pub_date=time)self.assertIs(future_question.was_published_recently(), False)

运行测试（指令是在项目跟目录执行的，该目录有 manage.py）

py manage.py test polls

• py manage.py test polls 将会寻找 polls 应用里的测试代码
• 查找 django.test.TestCase 子类
• 创建一个特殊的数据库供测试使用
• 在类中寻找测试方法——以 test 开头的方法。