如何检查django模板变量是否已定义？ [英] How to check if django template variable is defined?

问题描述

我有一个django模板，可用于许多视图。该模板有一个用于消息的块，用于通知用户任何应引起注意的消息。是否发送消息取决于视图。某些视图可能会向模板发送 message 变量，而其他视图则可能不会。

I have a django template which is used from many views. The template has a block for messages used to notify user of anything that should take their attention. Whether a message is sent or not depends on the views. Some views may send a message variable to the template while others may not.

view_1:
    message = "This is an important message"
    render_to_response("my_template.html", 
                       {'message':message, 'foo':foo, 'bar':bar},
                       context_instance = RequestContext(request))

view_2:
    message = "This is an important message"
    render_to_response("my_template.html", 
                       {'foo':foo, 'bar':bar},
                       context_instance = RequestContext(request))

在模板中，我检查了消息变量并包含以下块：

In the template, I check for the message variable and include the block as below:

base_template.html:
    ....
    {% block main_body %}
         {% block messages %}
         {% endblock %}
         {% block content %}
         {% endblock %}
    {% endblock %}
    ....

 my_template.html:
     {% extends base_template.html %}
     ....
     {% if message %}
          {% block messages %}
              <div class='imp_msg'>{{ message }} </div>
          {% endblock %}
     {% endif %}
     ...

问题在于，即使view_2没有传递消息，最终的html仍使用< div class ='imp_msg'>< / div> 呈现。 -基本上是一个空的div。

Problem is that even if view_2 does not pass a message, the final html is rendered with <div class='imp_msg'></div> -- basically an empty div.

由于CSS旨在为邮件提供浅红色背景，因此我看到的是页面顶部的空白light_red栏。

Since that CSS is designed to give a light_red background to messages, what I see is an empty light_red bar on the top of the page.

我也尝试过： {％ifnotequal message None％} ， {％ifnotequal message''％} ，尝试将消息设置为 None 或

I also tried: {% ifnotequal message None %}, {% ifnotequal message '' %}, tried setting the message to None or '' explicitly, but does not seem to help.

不胜感激！

推荐答案

您需要切换 {％block％} 和 {％if％}

{% block messages %}
    {% if message %}<div class='imp_message'>{{ message }}</div>{% endif %}
{% endblock %}

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