Question

大家好，我想按照此网站https://djangopy.org/how-to/how-to-implement-categories-in-django/上的教程为帖子添加类别系统（我对代码做了些改动）

每次尝试转到类别页面查看该类别内的帖子时，都会收到此错误'NoneType' object has no attribute 'threads'。

models.py：

from django.db import models
from django.urls import reverse
from django.utils.text import slugify

class Category(models.Model):
    name = models.CharField(max_length=100)
    short_desc = models.CharField(max_length=160)
    slug = models.SlugField()
    parent = models.ForeignKey('self', blank=True, null=True, related_name='children', on_delete=models.CASCADE)

    class Meta:
        unique_together = ('slug', 'parent',)
        verbose_name_plural = "Categories"

    def __str__(self):
        full_path = [self.name]
        k = self.parent

        while k is not None:
            full_path.append(k.name)
            k = k.parent

        return ' -> '.join(full_path[::-1])

    def save(self, *args, **kwargs):
        value = self.name
        self.slug = slugify(value, allow_unicode=True)
        super().save(*args, **kwargs)


class Thread(models.Model):
    ...
    category = models.ForeignKey('Category', null=True, blank=True, on_delete=models.CASCADE, related_name='threads')
    ...

    def get_cat_list(self):
        k = self.category
        breadcrumb = ["dummy"]
        while k is not None:
            breadcrumb.append(k.slug)
            k = k.parent

        for i in range(len(breadcrumb)-1):
            breadcrumb[i] = '/'.join(breadcrumb[-1:i-1:-1])
        return breadcrumb[-1:0:-1]

    ...

views.py：

from django.shortcuts import render, HttpResponseRedirect
from django.contrib import messages
from .models import Category, Thread
from .forms import SubmitScamNumber

def show_category_view(request, hierarchy=None):
    category_slug = hierarchy.split('/')
    category_queryset = list(Category.objects.all())
    all_slugs = [ x.slug for x in category_queryset ]
    parent = None
    for slug in category_slug:
        if slug in all_slugs:
            #parent = get_object_or_404(Category, slug=slug, parent=parent)
            parent = Category.objects.filter(slug__in=category_slug, parent=None).first()

    context = {
        'category': parent,
        'threads': parent.threads.all(),
        'sub_categories': parent.children.all(),
    }
    return render(request, "categories.html", context)

 ...

categories.html：

{% extends 'base.html' %}
{% block content %}

{% if sub_categories %}
    <h3>Sub Categories</h3>
    {% for i in sub_categories %}
        <a href="{{ i.slug }}"> {{ i.name }} </a>
    {% endfor %}
{% endif %}

{% if threads %}
{% for i in threads %}
    <div class="columns">
        <div class=" card-article-hover card">
          <a href="{{ i.slug }}">
            <img  src="{{ i.cover_photo.url }}">
          </a>
          <div class="card-section">
            <a href="{{ i.slug }}">
              <h6 class="article-title">{{ i.title | truncatechars:30}}</h6>
            </a>
          </div>
          <div class="card-divider flex-container align-middle">
            <a href="" class="author">{{ i.user.get_full_name }}</a>
          </div>
          <div class="hover-border">
          </div>
        </div>
    </div>
{% endfor %}
{% endif %}

{% endblock content %}

Answer 1

在show_category_view中设置parent = None。然后，如果有任何从hierarchy派生的块，则将它们循环并重新分配parent作为Category的实例。但是，如果在category_slug 或中没有任何标签，则在all_slugs 或中找不到该标签。返回Category.objects.filter(slug__in=category_slug, parent=None).first()的实例，则Category的值将保持为parent，然后当您尝试访问{{1}的对象上的None属性时}，就像您在这里所做的一样……

threads

...您看到的异常将会发生。

由于错误告诉您None，因为parent.threads.all() # parent = None仍然是最初定义的'NoneType' object has no attribute 'threads'。

此函数中还存在另一个null检查错误。

parent

您将None参数的默认值设置为def show_category_view(request, hierarchy=None): category_slug = hierarchy.split('/')，然后在其上调用hierarchy，即使该值可能是None。如果您在split上调用None，则会抛出类似的split。

您也不需要将None投射到AttributeError上。查询集已经像对象一样列出来了，可以被循环，实现迭代器协议等。（实际上，这样做可以丢弃查询集接口为您提供的所有好处。）在这里，您可以执行以下操作：

list

Django-'NoneType'对象没有属性'threads'

1 个答案: