当我不在我的 Django 博客文章中上传图像时防止 ValueError

Question

我有这个模型：

class News(models.Model):
    title = models.CharField(max_length=255)
    body = models.TextField()
    date = models.DateTimeField(auto_now_add=True)
    author = models.ForeignKey(
        get_user_model(),
        on_delete=models.CASCADE,
    )
    thumb = models.ImageField(blank=True)

    def __str__(self):
        return self.title

    def get_absolute_url(self):
        return reverse('news_detail', args=[str(self.id)])

如果我添加博客文章并包含图片，一切都很好。如果我不包含图像并尝试在浏览器中查看帖子，则会出现此错误：

raise ValueError("The '%s' attribute has no file associated with it." % self.field.name)
ValueError: The 'thumb' attribute has no file associated with it.
[01/Apr/2019 08:11:48] "GET /news/ HTTP/1.1" 500 178129

blank=True如果我不包含图像，我认为可以防止任何错误。我也尝试thumb = models.ImageField(blank=True, null=True)基于此问题但没有任何区别。

我怎样才能选择在我的博客文章中上传图片或不上传图片而不会出错？

附加信息

news_detail.html

{% extends 'base.html' %}

{% block content %}
    <div class="news-entry">
        <h2>{{ object.title }}</h2>
            <p>by {{object.author }} | {{ object.date }}</p>
            <p align="center"><img src="{{ object.thumb.url }}" /></p>
            <p>{{ object.body }}</p>
    </div>

    <p><a href="{% url 'news_edit' news.pk %}">Edit</a> |
       <a href="{% url 'news_delete' news.pk %}">Delete</a></p>
    <p>Back to <a href="{% url 'news_list' %}">All News</a>.</p>
{% endblock content %}

股票跟踪：

Internal Server Error: /news/2/

回溯（最近一次通话）：文件“/Users/me/.local/share/virtualenvs/lakelandcc-6nBitmwo/lib/python3.7/site-packages/django/template/base.py”，第 829 行，在 _resolve_lookup current = current[bit] TypeError: 'ImageFieldFile' 对象不可下标

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/me/.local/share/virtualenvs/lakelandcc-6nBitmwo/lib/python3.7/site-packages/django/core/handlers/exception.py", line 34, in inner
    response = get_response(request)
  File "/Users/me/.local/share/virtualenvs/lakelandcc-6nBitmwo/lib/python3.7/site-packages/django/core/handlers/base.py", line 156, in _get_response
    response = self.process_exception_by_middleware(e, request)
  File "/Users/me/.local/share/virtualenvs/lakelandcc-6nBitmwo/lib/python3.7/site-packages/django/core/handlers/base.py", line 154, in _get_response
    response = response.render()
  File "/Users/me/.local/share/virtualenvs/lakelandcc-6nBitmwo/lib/python3.7/site-packages/django/template/response.py", line 106, in render
    self.content = self.rendered_content
  File "/Users/me/.local/share/virtualenvs/lakelandcc-6nBitmwo/lib/python3.7/site-packages/django/template/response.py", line 83, in rendered_content
    content = template.render(context, self._request)
  File "/Users/me/.local/share/virtualenvs/lakelandcc-6nBitmwo/lib/python3.7/site-packages/django/template/backends/django.py", line 61, in render
    return self.template.render(context)
  File "/Users/me/.local/share/virtualenvs/lakelandcc-6nBitmwo/lib/python3.7/site-packages/django/template/base.py", line 171, in render
    return self._render(context)
  File "/Users/me/.local/share/virtualenvs/lakelandcc-6nBitmwo/lib/python3.7/site-packages/django/template/base.py", line 163, in _render
    return self.nodelist.render(context)
  File "/Users/me/.local/share/virtualenvs/lakelandcc-6nBitmwo/lib/python3.7/site-packages/django/template/base.py", line 937, in render
    bit = node.render_annotated(context)
  File "/Users/me/.local/share/virtualenvs/lakelandcc-6nBitmwo/lib/python3.7/site-packages/django/template/base.py", line 904, in render_annotated
    return self.render(context)
  File "/Users/me/.local/share/virtualenvs/lakelandcc-6nBitmwo/lib/python3.7/site-packages/django/template/loader_tags.py", line 150, in render
    return compiled_parent._render(context)
  File "/Users/me/.local/share/virtualenvs/lakelandcc-6nBitmwo/lib/python3.7/site-packages/django/template/base.py", line 163, in _render
    return self.nodelist.render(context)
  File "/Users/me/.local/share/virtualenvs/lakelandcc-6nBitmwo/lib/python3.7/site-packages/django/template/base.py", line 937, in render
    bit = node.render_annotated(context)
  File "/Users/me/.local/share/virtualenvs/lakelandcc-6nBitmwo/lib/python3.7/site-packages/django/template/base.py", line 904, in render_annotated
    return self.render(context)
  File "/Users/me/.local/share/virtualenvs/lakelandcc-6nBitmwo/lib/python3.7/site-packages/django/template/loader_tags.py", line 62, in render
    result = block.nodelist.render(context)
  File "/Users/me/.local/share/virtualenvs/lakelandcc-6nBitmwo/lib/python3.7/site-packages/django/template/base.py", line 937, in render
    bit = node.render_annotated(context)
  File "/Users/me/.local/share/virtualenvs/lakelandcc-6nBitmwo/lib/python3.7/site-packages/django/template/base.py", line 904, in render_annotated
    return self.render(context)
  File "/Users/me/.local/share/virtualenvs/lakelandcc-6nBitmwo/lib/python3.7/site-packages/django/template/base.py", line 987, in render
    output = self.filter_expression.resolve(context)
  File "/Users/me/.local/share/virtualenvs/lakelandcc-6nBitmwo/lib/python3.7/site-packages/django/template/base.py", line 671, in resolve
    obj = self.var.resolve(context)
  File "/Users/me/.local/share/virtualenvs/lakelandcc-6nBitmwo/lib/python3.7/site-packages/django/template/base.py", line 796, in resolve
    value = self._resolve_lookup(context)
  File "/Users/me/.local/share/virtualenvs/lakelandcc-6nBitmwo/lib/python3.7/site-packages/django/template/base.py", line 837, in _resolve_lookup
    current = getattr(current, bit)
  File "/Users/me/.local/share/virtualenvs/lakelandcc-6nBitmwo/lib/python3.7/site-packages/django/db/models/fields/files.py", line 61, in url
    self._require_file()
  File "/Users/me/.local/share/virtualenvs/lakelandcc-6nBitmwo/lib/python3.7/site-packages/django/db/models/fields/files.py", line 38, in _require_file
    raise ValueError("The '%s' attribute has no file associated with it." % self.field.name)
ValueError: The 'thumb' attribute has no file associated with it.
[01/Apr/2019 08:29:46] "GET /news/2/ HTTP/1.1" 500 160702

Answer 1

请在调用 url 之前检查图像是否存在

 <p align="center"><img src="{{ object.thumb.url }}" /></p>

到

{% if object.thumb %}
 <p align="center"><img src="{{ object.thumb.url }}" /></p>
{% endif %}