Django - 具有赋值的自定义标签答案

【问题标题】：Django - custom tags with assigning valuesDjango - 具有赋值的自定义标签
【发布时间】：2017-10-29 13:07:24
【问题描述】：

我正在尝试在 django 中构建自己的标签。

这是我定义标签时的代码：

@register.inclusion_tag('post/templates/comment_block')
def limit_amount_in_a_page(starting_index, topic_id=1, amount=5):
    comments = Comment.get_item_with_topic_id(topic_id)
    selected_comments = []
    for index in range(starting_index, starting_index+amount):
        selected_comments.append(comments[index])
    return {'selected_comments': selected_comments}

这就是我的使用方式：

<div class="past_comments">
    {% limit_amount_in_a_page starting_index=0 topic_id=1 amount=5 %}
</div>

这是模板：

<ul>
{% for comment in selected_comments %}
<li>
    <div class="comment_body">
    <div class="user_info_block">
        <div class="content">
            <div class="photo_profile"></div>
            <div class="user_info"></div>
        </div>
    </div>
    <div class="content_block">

        <p>{{comment.content}}</p>
    </div>
    </div>
</li>
{% endfor %}

但是，我得到了这个例外：

get_item_with_topic_id() 缺少 1 个必需的位置参数：'topic_id'

我尝试在没有变量名的块中使用标签，但仍然有同样的错误。

这是完整的追溯

Environment:
Request Method: GET
Request URL: http://127.0.0.1:8000/post/1/

Django Version: 1.11.3
Python Version: 3.6.2
Installed Applications:
['post.apps.PostConfig',
 'music.apps.MusicConfig',
 'django.contrib.admin',
 'django.contrib.auth',
 'django.contrib.contenttypes',
 'django.contrib.sessions',
 'django.contrib.messages',
 'django.contrib.staticfiles']
Installed Middleware:
['django.middleware.security.SecurityMiddleware',
 'django.contrib.sessions.middleware.SessionMiddleware',
 'django.middleware.common.CommonMiddleware',
 'django.middleware.csrf.CsrfViewMiddleware',
 'django.contrib.auth.middleware.AuthenticationMiddleware',
 'django.contrib.messages.middleware.MessageMiddleware',
 'django.middleware.clickjacking.XFrameOptionsMiddleware']


Template error:
In template                         C:\Users\Nutzer\PycharmProjects\selfTry\post\templates\post\detail.html, error         at line 16
   get_item_with_topic_id() missing 1 required positional argument: 'topic_id'   6 :     <meta charset="UTF-8">
   7 :     <title>{{topic.topic}}</title>
   8 :     <link rel="stylesheet" type="text/css" href="{% static 'post/comment_block.css' %}">
   9 :     <link rel="stylesheet" type="text/css" href="{% static 'post/detail_base.css' %}">
   10 : </head>
   11 : <body>
   12 :     <div class="topic">
   13 :         {{topic.topic}}
   14 :     </div>
   15 :     <div class="past_comments">
   16 :          {% limit_amount_in_a_page page_nr=0 topic_id=1 amount=5 %} 
   17 :         {% if starting_index is 0 %}
   18 :         <a href="#">Last Page</a>
   19 :         {% endif %}
   20 :         <a href="#">Next Page</a>
   21 :     </div>
   22 : 
   23 :     <div class="leave_a_comment">
   24 :         <form action = "{% url 'post:comment' topic_id=topic.id user_id=1 %}" method="post">
   25 :             {% csrf_token %}
   26 :             {{ form.as_p }}


Traceback:

File "C:\Users\Nutzer\AppData\Local\Programs\Python\Python36-32\lib\site-    packages\django\core\handlers\exception.py" in inner
  41.             response = get_response(request)

File "C:\Users\Nutzer\AppData\Local\Programs\Python\Python36-32\lib\site-packages\django\core\handlers\base.py" in _get_response
  187.                 response = self.process_exception_by_middleware(e, request)

File "C:\Users\Nutzer\AppData\Local\Programs\Python\Python36-32\lib\site-packages\django\core\handlers\base.py" in _get_response
  185.                 response = wrapped_callback(request, *callback_args, **callback_kwargs)

File "C:\Users\Nutzer\PycharmProjects\selfTry\post\views.py" in detail
  26.         'comments': comments,

File "C:\Users\Nutzer\AppData\Local\Programs\Python\Python36-32\lib\site-packages\django\shortcuts.py" in render
  30.     content = loader.render_to_string(template_name, context, request, using=using)

File "C:\Users\Nutzer\AppData\Local\Programs\Python\Python36-32\lib\site-packages\django\template\loader.py" in render_to_string
  68.     return template.render(context, request)

File "C:\Users\Nutzer\AppData\Local\Programs\Python\Python36-32\lib\site-packages\django\template\backends\django.py" in render
  66.             return self.template.render(context)

File "C:\Users\Nutzer\AppData\Local\Programs\Python\Python36-32\lib\site-packages\django\template\base.py" in render
  207.                     return self._render(context)

File "C:\Users\Nutzer\AppData\Local\Programs\Python\Python36-32\lib\site-packages\django\template\base.py" in _render
  199.         return self.nodelist.render(context)

File "C:\Users\Nutzer\AppData\Local\Programs\Python\Python36-32\lib\site-packages\django\template\base.py" in render
  990.                 bit = node.render_annotated(context)

File "C:\Users\Nutzer\AppData\Local\Programs\Python\Python36-32\lib\site-packages\django\template\base.py" in render_annotated
  957.             return self.render(context)

File "C:\Users\Nutzer\AppData\Local\Programs\Python\Python36-32\lib\site-packages\django\template\library.py" in render
  225.         _dict = self.func(*resolved_args, **resolved_kwargs)

File "C:\Users\Nutzer\PycharmProjects\selfTry\post\templatetags\post_tags.py" in limit_amount_in_a_page
  13.     comments = Comment.get_item_with_topic_id(topic_id)

Exception Type: TypeError at /post/1/
Exception Value: get_item_with_topic_id() missing 1 required positional     argument: 'topic_id'

然后是从sqlite中获取item的方法

class Comment(models.Model):
class Meta:
    unique_together = (('commenter_id', 'date'),)

topic = models.ForeignKey(Topic, on_delete=models.CASCADE)
commenter_id = models.IntegerField()
date = models.DateTimeField(auto_now=True)
content = models.CharField(max_length=9999999)

def __str__(self):
    return "comment from " + str(self.commenter_id) + " on " + str(self.date)

def get_item_with_topic_id(self, topic_id):
    comments = self.objects.get(id=topic_id)
    return comments

【问题讨论】：

请显示完整的回溯。
@DanielRoseman 添加了
你能不能也显示那个get_item_with_topic_id方法的定义？
@DanielRoseman 当然！

标签： python django tags backend

【解决方案1】：

这个问题其实和模板标签无关。

您已将get_item_with_topic_id 定义为实例方法，该方法将self 作为其第一个参数。但是您直接在 Comment 类上调用它，因此不涉及实例并且未传递 self - 因此 Python 认为您传递 topic_id 的值代替 self 而没有传递 @ 987654326@。

您可以通过将其声明为类方法并使用cls 而不是self 来解决此问题，但您不应该这样做；像这样的自定义查询方法属于 Manager，而不是模型。所以：

class CommentManager(models.Manager):
  def get_item_with_topic_id(self, topic_id):
    comments = self.get(id=topic_id)
    return comments

class Comment(models.Model): 
  ...
  objects = CommentManager()

现在你的模板标签可以调用Comment.objects.get_item_with_topic_id。

（顺便问一句，你确定查询是对的吗？不应该是.get(topic_id=topic_id)吗？）

【讨论】：

它帮助了我的问题！谢谢你！对于那个id，我使用默认的pk，所以自动叫id