How to perform basic conditional judgments in AnQiCMS templates, such as checking if a variable exists?

Mastering Content Wisdom: The Art of Variable Judgment in AnQiCMS Templates

In the world of websites built with AnQiCMS, the template is the stage for content, and how to make the elements on this stage intelligently display according to different conditions is the core skill that every operations expert and developer needs to master.As an enterprise-level content management system based on Go language and supporting syntax similar to Django template engine, AnQiCMS provides intuitive and powerful template tags, among which the most fundamental and commonly used are variable conditional judgments, especially the judgment of whether a variable exists or has a value.

Imagine if your website needs to display an author's avatar on an article detail page, but some articles may not have set one;Or, a product list page where you only want to display the dropdown menu when there are subcategories.These scenarios cannot do without observing the variables. Today, let's delve into how to make elegant basic conditional judgments in the AnQiCMS template, especially how to determine if a variable exists and has a value.

I. Basic Conditional Judgment in AnQiCMS Templates

The template syntax of AnQiCMS follows the style of Django template engine, using conditional judgment{% if ... %}Label pair. It allows us to determine whether to render a specific content block based on the truth or falsity of an expression. A complete conditional judgment structure typically includes{% if %}, optional{% elif %}(else if) and{% else %}, and the final{% endif %}To end the judgment.

For example, a simple judgment might be like this:

{% if archive.Id == 10 %}
    <p>这是文档ID为10的文档的特别内容。</p>
{% else %}
    <p>这不是文档ID为10的文档。</p>
{% endif %}

This structure provides the basic framework for controlling the display of page elements. We can also cleverly use this to determine whether a variable exists or has a value.{% if %}.

Chapter 2: Core Techniques and Practices for Checking Variable Existence and Value

In the AnQiCMS template, determining whether a variable exists or has a value depends mainly on the template engine's understanding of 'truthy' and 'falsy' values. When a variable is defined but its value is an empty string, 0,nilAn empty value, or an empty collection (such as an empty array, empty slice, or empty dictionary), is considered a 'false value' by the template engine; otherwise, it is considered a 'true value'.

1. Directly judge the variable name: The most concise "exists" judgment

The most direct way to determine if a variable exists or has a value is to place it in{% if %}In the label. If the variable exists and is considered a "true" value, the condition is met.

Suppose we are displaying a document and we want to show a thumbnail only if the document is set to display one.ThumbIt will display when this is true:

{% if archive.Thumb %}
    <img src="{{ archive.Thumb }}" alt="{{ archive.Title }}" />
{% else %}
    <p>暂无缩略图。</p>
{% endif %}

Here, archive.ThumbIf it is a valid image URL string, it is 'true', and the image will display. Ifarchive.Thumbit is an empty string ornilIt is the 'false value', which will display 'no thumbnail available'. This is a concise and efficient method commonly used in template development.

The same logic also applies to判断数字、布尔值等：

{# 如果 archive.Views（浏览量）大于0，则显示 #}
{% if archive.Views %}
    <span>浏览量：{{ archive.Views }}</span>
{% endif %}

{# 如果 item.IsCurrent（是否当前）为true，则添加active类 #}
<li class="{% if item.IsCurrent %}active{% endif %}">
    <a href="{{ item.Link }}">{{ item.Title }}</a>
</li>

2. Check if the set (list) is empty：{% for ... empty %}elegant use

When we need to judge a set (such asarchiveListorcategoryListWhether the returned list contains an element, besides using{% if collection_name %}AnQiCMS also provides a more elegant and semantically meaningful{% for ... empty %}the structure.

This structure allows you to execute when traversing a collection if the collection is empty{% empty %}The content of the block:

{% archiveList archives with type="list" categoryId="1" limit="10" %}
    {% for item in archives %}
        <li><a href="{{ item.Link }}">{{ item.Title }}</a></li>
    {% empty %}
        <li>该分类下没有任何文档。</li>
    {% endfor %}
{% endarchiveList %}

This code clearly expresses the logic of 'if there is a document, traverse and display it, otherwise prompt that there is no content', avoiding extra{% if %}judgment, making the code more compact and readable.

3. Use to judge a variable does not exist (negative judgment):{% if not %}

Sometimes, we may need to judge a variableNotwhether it exists orNoneexecute certain operations. At this time, you can add before the variablenotkeywords.

For example, on the article detail page, we often display "Previous" and "Next" links. If the current article does not have a previous or next article, we usually display "None" or do not display the link:

{% prevArchive prev %}
    <div>
        上一篇：
        {% if not prev %}
            <span>没有了</span>
        {% else %}
            <a href="{{ prev.Link }}">{{ prev.Title }}</a>
        {% endif %}
    </div>
{% endprevArchive %}

{% nextArchive next %}
    <div>
        下一篇：
        {% if not next %}
            <span>没有了</span>
        {% else %}
            <a href="{{ next.Link }}">{{ next.Title }}</a>
        {% endif %}
    </div>
{% endnextArchive %}

{% if not prev %}Will judgeprevWhether the variable is a 'false value' (i.e., does not exist or is empty), thus deciding to display a prompt or the actual link.

4. UsedefaultThe filter provides default values: display judgment.

In addition to controlling the display of content blocks, sometimes we just want to display a preset default text when a variable has no value, rather than controlling the logic of the entire code block. At this point, we can usedefaultfilter.

defaultThe filter will return the default value you specify when the variable is a "false value". Please note that this will not change the rendering logic of the template, it just provides an alternative display content.

<p>作者：{{ archive.Author|default:"佚名" }}</p>
<p>发布日期：{{ stampToDate(archive.CreatedTime, "2006-01-02")|default:"未知日期" }}</p>

In this example, ifarchive.AuthorNo value, the page will display "Anonymous"; ifarchive.CreatedTimeUnable to be formatted (for example, a value of 0 or nil), then display "Unknown Date". This is especially suitable for optional text information that does not affect the core layout of the page.

In addition, there is another.default_if_noneA filter that is stricter, only providing default values when the variable is in Go language.nil(null pointer) and does not provide default values likedefaultSuch also works for empty strings, 0, etc. In most web template scenarios,defaultusually is enough to use.

Third, the application combined with actual scenarios.

You have mastered these basic conditional judgment skills, and you can control the display of content in the AnQiCMS template with ease:

• **Lazy loading of image resources