Django入门项目实践（上）

项目结构

1.建立项目

File -->> New Project...

第一个Location是项目所在的目录，第二个Location是项目独立的Python运行环境，我们称之为Virtualenv。
Base interpreter是Python安装目录下的python.exe。
刚创建的Django项目如下所示：

在Terminal窗口输入命令python manage.py runserver也可以启动项目。

在浏览器中访问http://127.0.0.1:8000/，看到下面这个页面表明项目到目前为止一切正常。

2.创建应用程序

Django项目由一系列应用程序组成，它们协同工作，让项目成为一个整体。
实际上，PyCharm的Terminal窗口已经处于Django项目独立的运行环境，执行python manage.py startapp learning_logs命令创建一个应用程序：

创建完应用程序后，就可以在项目中看到新增的应用程序的目录。

2.1 定义模型

# untitled/learning_logs/models.py
from django.db import models


class Topic(models.Model):
    """A topic the user is learning about."""
    text = models.CharField(max_length=200)
    date_added = models.DateTimeField(auto_now_add=True)

    def __str__(self):
        """Return a string representation of the model."""
        return self.text


class Entry(models.Model):
    """Something specific learned about a topic."""
    topic = models.ForeignKey('Topic', on_delete=models.CASCADE)
    text = models.TextField()
    date_added = models.DateTimeField(auto_now_add=True)

    class Meta:
        verbose_name_plural = 'entries'

    def __str__(self):
        """Return a string representation of the model."""
        return self.text[:50] + "..."

2.2 激活模型

# untitled/untitled/settings.py
# ···
# Application definition

INSTALLED_APPS = [
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',

    # 我的应用程序
    'learning_logs',
]

# ···

2.3 创建数据库

接着，先后执行命令python manage.py makemigrations learning_logs和python manage.py migrate，前者生成一个文件0001_initial.py告诉Django如何修改数据库，后者就让Django修改数据库了。

2.4 Django管理网站

为应用程序定义模型时，Django提供的管理网站让你能够轻松地处理模型。
创建超级用户：

向管理网站注册模型：

# untitled/learning_logs/admin.py
from django.contrib import admin

# Register your models here.
from learning_logs.models import Topic, Entry

admin.site.register(Topic)
admin.site.register(Entry)

使用超级用户访问管理网站http://127.0.0.1:8000/admin/。

我们可以在管理网站管理模型的数据：

2.5 Django shell

输入一些数据后，就可通过交互式终端会话以编程方式查看这些数据了。这种交互式环境称为Django shell，是测试项目和排除其故障的理想之地。

3.创建网页

使用Django创建网页的过程通常分三个阶段：定义URL、编写视图和编写模板。
每个URL都被映射到特定的视图——视图函数获取并处理网页所需的数据。视图函数通常调用一个模板，后者生成浏览器能够理解的网页。

3.1 映射URL

http://127.0.0.1:8000/默认返回Django网站，我们修改这一点，将这个URL映射到“学习笔记”的主页。

# untitled/untitled/urls.py
from django.contrib import admin
from django.urls import path
from django.conf.urls import include, url

urlpatterns = [
    path('admin/', admin.site.urls),
    url(r'', include('learning_logs.urls', namespace='learning_logs'))
]

"""定义learning_logs的URL模式"""

# untitled/learning_logs/urls.py
from django.conf.urls import url

from . import views

app_name = 'learning_logs'

urlpatterns = [
    # 主页
    url(r'^$', views.index, name='index'),
]

3.2 编写视图

# untitled/learning_logs/views.py
from django.shortcuts import render

# Create your views here.


def index(request):
    """学习笔记的主页"""
    return render(request, 'learning_logs/index.html')

3.3 编写模板

<!-- untitled/templates/learning_logs/index.html -->
<p>Learning Log</p>

<p>Learning Log helps you keep track of your learning, for my topic you're learning about.</p>

3.3.1 父模板

<!-- untitled/templates/learning_logs/base.html -->
<p>
  <a href="{% url 'learning_logs:index' %}">Learning Log</a>
</p>

{% block content %}{% endblock %}

3.3.2 子模板

<!-- untitled/templates/learning_logs/index.html -->
{% extends "learning_logs/base.html" %}

{% block content %}
  <p>Learning Log helps you keep track of your learning, for any topic you're
  learning about.</p>
{% endblock content %}

显示所有主题的页面

"""定义learning_logs的URL模式"""

# untitled/learning_logs/urls.py
from django.conf.urls import url

from . import views

app_name = 'learning_logs'

urlpatterns = [
    # 主页
    url(r'^$', views.index, name='index'),
    url(r'^topics/$', views.topics, name='topics'),
]

# untitled/learning_logs/views.py

#···

def topics(request):
    topics = Topic.objects.order_by('date_added')
    context = {'topics' : topics}
    return render(request, 'learning_logs/topics.html', context)

# ···

<!-- untitled/templates/learning_logs/topics.html -->
{% extends "learning_logs/base.html" %}

{% block content %}

  <p>Topics</p>

  <ul>
    {% for topic in topics %}
      <li>{{ topic }}</li>
    {% empty %}
      <li>No topics have been added yet.</li>
    {% endfor %}
  </ul>

{% endblock content %}

显示特定主题的页面

"""定义learning_logs的URL模式"""

# untitled/learning_logs/urls.py
from django.conf.urls import url

from . import views

app_name = 'learning_logs'

urlpatterns = [
    # 主页
    url(r'^$', views.index, name='index'),
    url(r'^topics/$', views.topics, name='topics'),
    url(r'^topics/(?P<topic_id>\d+)/$', views.topic, name='topic'),
]

# untitled/learning_logs/views.py

#···

def topic(request, topic_id):
    """Show a single topic, and all its entries."""
    topic = Topic.objects.get(id=topic_id)
    entries = topic.entry_set.order_by('-date_added')
    context = {'topic': topic, 'entries': entries}
    return render(request, 'learning_logs/topic.html', context)

#···

<!-- untitled/templates/learning_logs/topic.html -->
{% extends 'learning_logs/base.html' %}

{% block content %}

  <p>Topic: {{ topic }}</p>

  <p>Entries:</p>
  <ul>
  {% for entry in entries %}
    <li>
      <p>{{ entry.date_added|date:'M d, Y H:i' }}</p>
      <p>{{ entry.text|linebreaks }}</p>
    </li>
  {% empty %}
    <li>
      There are no entries for this topic yet.
    </li>
  {% endfor %}
  </ul>

{% endblock content %}

参考资料：《Python编程从入门到实践》—【美】Eric Matthes 著