Django实践：创建表单，debug--NoReverseMatch at /topics/1/和Page not found (404)，分析与解决_django page not found

Django实践：创建表单

创建表单步骤

1. 在当前应用中添加一个新的forms.py，在里面创建表单，包括主题和条码项

from django import forms
from .models import Topic, Entry

class TopicForm(forms.ModelForm):
    class Meta:
        model = Topic
        fields = ['text']
        labels = {'text': ''}

class EntryForm(forms.ModelForm):
    class Meta:
        model = Entry
        fields = ['text']
        labels = {'text': ''}
        widgets = {'text': forms.Textarea(attrs={'cols': 80})}
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2. 映射URL，在urls.py中添加Topic和Entry的url模式

    # Page for adding a new topic.
    re_path('^new_topic/$', views.new_topic, name='new_topic'),

    # Page for adding a new entry.
    re_path('^new_entry/(?P<topic_id>\d+)/$', views.new_entry, name='new_entry'),
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3. 编写视图函数，在views.py中

from django.shortcuts import render
from django.http import HttpResponseRedirect, Http404
from django.urls import reverse

from .models import Topic, Entry
from .forms import TopicForm, EntryForm

def new_topic(request):
    """Add a new topic."""
    if request.method != 'POST':
        # No data submitted; create a blank form.
        form = TopicForm()
    else:
        # POST data submitted; process data.
        form = TopicForm(request.POST)
        if form.is_valid():
            form.save()
            return HttpResponseRedirect(reverse('learning_logs:topics'))

    context = {'form': form}
    return render(request, 'learning_logs/new_topic.html', context)


def new_entry(request, topic_id):
    """Add a new entry for a particular topic."""
    topic = Topic.objects.get(id=topic_id)

    if request.method != 'POST':
        # No data submitted; create a blank form.
        form = EntryForm()
    else:
        # POST data submitted; process data.
        form = EntryForm(data=request.POST)
        if form.is_valid():
            form.save()
            return HttpResponseRedirect(reverse('learning_logs:topic',
                                                args=[topic_id]))

    # context = {'topic': topic, 'form': form, 'topic_id': topic_id}
    context = {'topic': topic, 'form': form}
    return render(request, 'learning_logs/new_entry.html', context)
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4. 新建new_topic的模板new_topic.html，并在topics.html中添加new_topic的链接

<a href="{% url 'learning_logs:new_topic'%}">Add a new Topic:</a>
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5. 新建new_entry的模板new_entry.html，并在topic.html中添加new_entry的链接

<a href="{% url 'learning_logs:new_entry' topic.id %}">Add a new Entry:</a>
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debug

错误一：NoReverseMatch at /topics/1/

  Reverse for ‘new_entry’ with no arguments not found. 1 pattern(s) tried: [‘new_entry/(?P<topic_id>\d+)/$’]

  分析：反解析‘new_entry’时候未找到没有参数的‘new_entry’，因为views.py中的new_entry(request, topic_id)函数有另外的参数topic_id，说明在调用的时候没有将topic_id的参数传给views.py中的函数，也没有传给urls.py中的re_path()函数。

  解决：错误是在topic.html中，在向topic.html中添加new_entry页面链接的时候，未把topic_id参数传递给new_entry的re_path()函数和new_entry(request, topic_id)函数。

  错误代码如下：

<a href="{% url 'learning_logs:new_entry'%}">Add a new Entry:</a>
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  修改后：

<a href="{% url 'learning_logs:new_entry' topic.id %}">Add a new Entry:</a>
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错误二：Page not found (404)

  进入topic页面点击Add a new Entry链接时候，出现找不到页面的情况:

  分析：页面的链接不对
  解决：错误是在topic.html中，在%和}多了一个空格，导致超链接解析错误。

  错误代码如下：

<a href="{% url 'learning_logs:new_entry' topic.id % }">Add a new Entry:</a>
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  修改后：

<a href="{% url 'learning_logs:new_entry' topic.id %}">Add a new Entry:</a>
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参考文献

1. 《Python编程从入门到实践》：https://ehmatthes.github.io/pcc/
2. Django帮助文档：https://docs.djangoproject.com/zh-hans/2.0/