课程展示与缓存优化

本章将介绍如何在Django中实现课程展示页面、学生注册系统以及缓存优化。主要内容包括：

• 创建课程展示视图。
• 实现学生注册和选课功能。
• 渲染课程内容并支持多种媒体类型。
• 通过Memcached优化性能。

1. 展示课程列表

首先，我们需要展示所有可用的课程，并允许用户按主题筛选。以下是实现步骤：

# courses/views.py
from django.db.models import Count
from django.views.generic import View
from .models import Subject, Course

class CourseListView(View):
    template_name = 'courses/course/list.html'

    def get(self, request, subject=None):
        subjects = Subject.objects.annotate(total_courses=Count('course_set'))
        courses = Course.objects.annotate(total_modules=Count('module_set'))

        if subject:
            subject_instance = get_object_or_404(Subject, slug=subject)
            courses = courses.filter(subject=subject_instance)

        return render(request, self.template_name, {
            'subjects': subjects,
            'subject': subject_instance if subject else None,
            'courses': courses
        })

接下来，在`urls.py`中配置路由：

# educa/urls.py
from django.urls import path
from courses.views import CourseListView

urlpatterns = [
    path('', CourseListView.as_view(), name='course_list'),
    path('subject//', CourseListView.as_view(), name='course_list_subject'),
]

2. 学生注册与选课

为了允许学生注册并选择课程，我们创建一个新的应用`students`：

python manage.py startapp students

编辑`settings.py`激活新应用：

INSTALLED_APPS += ['students.apps.StudentsConfig']

然后定义注册视图：

# students/views.py
from django.contrib.auth.forms import UserCreationForm
from django.urls import reverse_lazy
from django.views.generic.edit import CreateView

class StudentRegistrationView(CreateView):
    form_class = UserCreationForm
    template_name = 'students/student/registration.html'
    success_url = reverse_lazy('student_course_list')

    def form_valid(self, form):
        response = super().form_valid(form)
        user = authenticate(username=form.cleaned_data['username'], password=form.cleaned_data['password1'])
        login(self.request, user)
        return response

接着，为选课功能添加逻辑：

# courses/models.py
class Course(models.Model):
    # ...
    students = models.ManyToManyField(User, related_name='enrolled_courses', blank=True)

# students/forms.py
from django import forms
from courses.models import Course

class EnrollForm(forms.Form):
    course = forms.ModelChoiceField(queryset=Course.objects.all(), widget=forms.HiddenInput)

# students/views.py
from django.contrib.auth.mixins import LoginRequiredMixin
from django.views.generic.edit import FormView

class EnrollCourseView(LoginRequiredMixin, FormView):
    form_class = EnrollForm

    def form_valid(self, form):
        course = form.cleaned_data['course']
        course.students.add(self.request.user)
        return super().form_valid(form)

    def get_success_url(self):
        return reverse_lazy('student_course_detail', args=[self.kwargs['pk']])

3. 渲染课程内容

通过多对多关系，学生可以访问已选课程的内容。以下是如何处理不同类型的课程内容：

# courses/models.py
from django.template.loader import render_to_string

class ContentBaseModel(models.Model):
    def render_content(self):
        return render_to_string(f'courses/content/{self.__class__.__name__.lower()}.html', {'item': self})

同时，为每种内容类型创建模板文件：

# courses/templates/courses/content/text.html
{{ item.text|linebreaks }}

# courses/templates/courses/content/file.html
<a href="{{ item.file.url }}" download>Download File</a>

# courses/templates/courses/content/image.html
<img src="{{ item.image.url }}" alt="{{ item.title }}">

# courses/templates/courses/content/video.html
{% load embed_video_tags %}
{% video item.video 'small' %}

4. 缓存优化

最后，我们使用Memcached来缓存查询结果和视图输出：

# settings.py
CACHES = {
    'default': {
        'BACKEND': 'django.core.cache.backends.memcached.MemcachedCache',
        'LOCATION': '127.0.0.1:11211',
    }
}

# courses/views.py
from django.core.cache import cache

class CachedCourseListView(CourseListView):
    def get(self, request, *args, **kwargs):
        cached_data = cache.get('all_courses')
        if not cached_data:
            cached_data = super().get(request, *args, **kwargs)
            cache.set('all_courses', cached_data, timeout=600)
        return cached_data