django入门-part4

Posted 2020-09-03 运维从入门到放弃

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完全翻译自官方文档 https://docs.djangoproject.com/en/1.10/intro/tutorial04/

本节内容讲表单

让我们更新一下pools/detail.html,添加html表单的展示

<h1>{{ question.question_text }}</h1>

{% if error_message %}<p><strong>{{ error_message }}</strong></p>{% endif %}

<form action="{% url ‘polls:vote‘ question.id %}" method="post">
{% csrf_token %}
{% 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 %}
<input type="submit" value="Vote" />
</form>

解释一下上面的代码:

form里添加了一个radio单选框,label是单选框的标签,每个单选框的值是 choice.id,当你点了"submit"提交表单时,实际提交的内容是

一个变量choice=choice.id 即 input的name和value,表单提交的方法必须是post

forloop.counte是for循环的一个计数器,表示循环了多少次

{% csrf_token %} 这个是用来防止跨站攻击的,django已经帮我们做好了,放在form上就可以了

提交这个表单时,匹配的url是这个

url(r‘^(?P<question_id>[0-9]+)/vote/$‘, views.vote, name=‘vote‘),

现在更新一下我们的vote的视图

from django.shortcuts import get_object_or_404, render
from django.http import HttpResponseRedirect, HttpResponse
from django.urls import reverse

from .models import Choice, 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):
        # Redisplay the question voting form.
        return render(request, ‘polls/detail.html‘, {
            ‘question‘: question,
            ‘error_message‘: "You didn‘t select a choice.",
        })
    else:
        selected_choice.votes += 1
        selected_choice.save()
        # Always return an HttpResponseRedirect after successfully dealing
        # with POST data. This prevents data from being posted twice if a
        # user hits the Back button.
        return HttpResponseRedirect(reverse(‘polls:results‘, args=(question.id,)))

解释request.POST 你用post提交表单时传的参数就是用这个接收,是一个字典类型的;对应的request.GET就是接收get请求的参数

request.POST[‘choice‘]当key不存在时,会抛一个KeyError异常,所以代码要捕获这个异常
HttpResponseRedirect(url)当成功提交表单返回结果时就用这个函数
reverse这个函数是为了避免url的硬编码,本来这个url应该是这样的

url(r‘^(?P<question_id>[0-9]+)/results/$‘, views.results, name=‘results‘),
现在呢

reverse(‘polls:results‘, args=(question.id,) 看不明白的请去复习上一节的内容(urls.py里的app_name和url()里的name就是这个用处

现在来完成result的视图

from django.shortcuts import get_object_or_404, render


def results(request, question_id):
    question = get_object_or_404(Question, pk=question_id)
    return render(request, ‘polls/results.html‘, {‘question‘: question})

result的视图有了,下面写展示的模板

<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>

这个例子就是你选择单选按钮,然后点击提交按钮,跳转到一个新的页面,没有使用ajax.

注意:

vote视图这里有并发问题,当多个人对同一个question投票时,数据库在存和取时就有资源竞争问题了

django的解决方案在此 https://docs.djangoproject.com/en/1.10/ref/models/expressions/#avoiding-race-conditions-using-f

厉害的来了

通用视图

考虑一下我们前面写的视图detail(),results(),index()都是web开发中最通用的操作,根据url的参数从数据库存取内容,然后模板展示,这就是django通用视图考虑的问题,下面让我们用通用视图修改一下我们前面的应用pools

先修改urls.py

from django.conf.urls import url

from . import views

app_name = ‘polls‘
urlpatterns = [
    url(r‘^$‘, views.IndexView.as_view(), name=‘index‘),
    url(r‘^(?P<pk>[0-9]+)/$‘, views.DetailView.as_view(), name=‘detail‘),
    url(r‘^(?P<pk>[0-9]+)/results/$‘, views.ResultsView.as_view(), name=‘results‘),
    url(r‘^(?P<question_id>[0-9]+)/vote/$‘, views.vote, name=‘vote‘),
]

修改视图views.py

from django.shortcuts import get_object_or_404, render
from django.http import HttpResponseRedirect
from django.urls import reverse
from django.views import generic

from .models import Choice, Question


class IndexView(generic.ListView):
    template_name = ‘polls/index.html‘
    context_object_name = ‘latest_question_list‘

    def get_queryset(self):
        """Return the last five published questions."""
        return Question.objects.order_by(‘-pub_date‘)[:5]


class DetailView(generic.DetailView):
    model = Question
    template_name = ‘polls/detail.html‘


class ResultsView(generic.DetailView):
    model = Question
    template_name = ‘polls/results.html‘


def vote(request, question_id):
    ... # same as above, no changes needed.