How to determine if a variable is empty in AnQiCMS template and display default content?

In website content operation, the integrity of data and the elegance of display are crucial.We often encounter such situations: some fields of data may be missing for various reasons, such as an article may not have an illustration, a product may not have a detailed description, or a custom field may not be filled in.If the template code does not make the corresponding null value judgment, it may cause the page to appear blank, affecting aesthetics, or even trigger template rendering errors, affecting user experience.

AnQiCMS with its efficient architecture based on the Go language and flexible design similar to the Django template engine, provides us with various powerful and intuitive ways to determine if a variable in the template is empty and display default content accordingly, allowing the website to maintain a good user experience even when data is incomplete.Let's explore these practical skills together.

Most intuitive and powerful: {% if ... %}logical judgment tag

In the AnQiCMS template,ifTags are the core tools we use for conditional judgment. They can determine whether a variable is 'true' or 'false'. A variable is considered a 'false' value when it is an empty string""numbers0and a boolean valuefalseand in Go languagenilequivalent to other languagesnullorNone)ifthe statement will execute itselseBlock content.

Basic usage:

Assume you have an article objectarchiveincludingTitle(Title) andDescription(description) etc. You can judge it like thisTitlewhether it is empty:

{% if archive.Title %}
    <h1>{{ archive.Title }}</h1>
{% else %}
    <h1>暂无标题</h1>
{% endif %}

Ifarchive.TitleNot empty, the page will display the actual title; otherwise, it will display 'No title'. Similarly, you can also useif notto determine if a variable is empty:

{% if not archive.Description %}
    <p>该文章暂无详细描述。</p>
{% else %}
    <p>{{ archive.Description }}</p>
{% endif %}

This method is suitable for scenarios where you need to display the entire HTML block or perform more complex logic.

Shortcut:defaultFilter

When you only need to provide a default value in the output, without the need for complex logical judgment structures,defaultThe filter is your **choice. It is concise and efficient, making the code more readable.

defaultThe filter will be applied when a variable is evaluated as a 'falsy' value (including an empty string""numbers0and a boolean valuefalseas well asnil)，display the default content you provided.

Usage example:

<p>作者：{{ archive.Author|default:"佚名" }}</p>
<img src="{{ archive.Logo|default:'/static/images/default_logo.png' }}" alt="{{ archive.Title|default:'文章图片' }}" />
<p>价格：{{ product.Price|default:0 }} 元</p>

In the above example:

• Ifarchive.AuthorEmpty, 'Anonymous' will be displayed.
• Ifarchive.LogoEmpty (or invalid), 'Unknown' will be displayed./static/images/default_logo.pngAs the default image.
• Ifproduct.PriceEmpty or0It will display0yuan.

defaultThe filter is very suitable for inline output, it can effectively avoid blank or broken links appearing on the page.

For the list:{% for ... %}Combine{% empty %}

When processing list data, especially when it is necessary to judge whether the list is empty and display a prompt message,forrepeatedlyemptyThe block is very practical. It provides an elegant way to handle the case where the list is empty, avoiding redundancy.ifjudgment.

Usage example:

Assuming you want to display a list of related documents, but sometimes it may not find related content:

{% archiveList relatedArchives with type="related" limit="5" %}
    {% for item in relatedArchives %}
        <div class="related-item">
            <a href="{{ item.Link }}">{{ item.Title }}</a>
        </div>
    {% empty %}
        <div class="no-related-content">暂无相关文档。</div>
    {% endfor %}
{% endarchiveList %}

IfrelatedArchivesThe list is empty or does not exist,emptyThe content within the block will be rendered, prompting the user that there is no relevant content, rather than leaving an empty area.

More accurate judgment:default_if_noneFilter

In certain specific scenarios, you may need to distinguish between a variable that does not exist at allnilor is merely empty (such as an empty string)""numbers0. In this casedefault_if_noneThe filter comes into play.

default_if_nonethe filter will only be applied if the variable's value isnilWhen it displays default content. This means it will not affect an empty string""or numbers0Take effect.

Usage example:

Assuming there is a custom fieldproduct.SpecificationIt may benil(Not set), or may also be""(Set but content is empty).

<p>产品规格（default）：{{ product.Specification|default:"未填写" }}</p>
<p>产品规格（default_if_none）：{{ product.Specification|default_if_none:"未设置" }}</p>

• Ifproduct.SpecificationIsnil:
  • The first line will display "Not filled in."
  • The second line will display "Not set."
• Ifproduct.SpecificationIs""(Empty string):
  • The first line will display "Not filled in."
  • The second line will display an empty string (i.e., no content will be displayed).

This filter is very useful when it is necessary to strictly differentiate between "unassigned" and "assigned but empty" scenarios.

Combining practical **practice

• Images and links:For imagessrcProperties and linkshrefProperties, usedefaultThe filter provides an alternative image or link to prevent the appearance of a 'broken link' icon or inaccessible links.
• Rich text content:For article details, product descriptions, and other rich text content, it is usually better to hide the area directly or display a "No content" prompt when the content is empty, at this time{% if ... %}CombinesafeThe filter (used for safely rendering HTML content) would be a better choice:

  
  {% if archive.Content %}
      <div class="article-content">{{ archive.Content|safe }}</div>
  {% else %}
      <div class="article-content">暂无详细内容。</div>
  {% endif %}
  

• Custom field:AnQiCMS is a powerful content model that allows us to create various custom fields. When calling these fields in the template, it is also necessary to make proper null value judgments.

  
  {% archiveDetail author with name="author" %}
  {% if author %}
      <p>作者：{{ author }}</p>
  {% else %}
      <p>作者信息待补充。</p>
  {% endif %}
  

By flexibly using these methods to judge whether variables are empty, you can write more robust and better user experience code.