How to set a reliable default value for empty variables in the Anqi CMS template?

As a senior website operations expert, I know that handling null variables is a key factor in ensuring the quality of website content and user experience when building and maintaining website templates.In such a flexible and efficient content management system as AnQiCMS, the flexible use of template variables is its strength. However, at the same time, how to elegantly set reliable default values for possibly empty variables to avoid ugly blank spaces or functional anomalies is an art worth in-depth exploration.

Today, we will share some practical and efficient strategies on how to set reliable default values for empty variables in the AnQi CMS template.

Why would an empty variable become a problem?

During the operation of the website, content uncertainty is the norm.For example, an article may not have any illustrations, a product description may be temporarily missing, or a custom field may not be applicable to some content types.When these corresponding variables in the template are empty, if the template is not handled properly, the front-end page will directly display blank, or output some unfriendly placeholders. This not only ruins the overall aesthetics of the website, reduces user experience, but may also affect SEO performance, because search engines also prefer content that is complete and structured clearly.Therefore, setting a default value for a possibly empty variable is an important guarantee to enhance the robustness and user satisfaction of the website.

AnQiCMS uses syntax similar to Django template engine, and its variable output uses double curly braces{{变量}}，Logical control uses single curly braces and the percent sign{% 标签 %}。This syntax provides powerful flexibility and offers us various clever methods for handling empty variables.

Method one: usedefaultanddefault_if_noneFilter, the simplest default setting

In AnQiCMS templates,defaultanddefault_if_noneThis is the most direct and concise way to handle empty variables. They are all used as filters (filters) and can easily provide alternative content for variables.

1.defaultFilter

defaultFilter applies to variables that arenilThe cases of 'falsy' values such as empty strings, empty lists, or empty dictionaries, etc. It is the most commonly used default value setting method, which can cover the vast majority of empty value scenarios.

  • Usage: {{ 变量 | default:"你的默认值" }}
  • Example:The article title variable is assumed to existarchive.TitleAnd a description variable for the articlearchive.Description.
<h1>{{ archive.Title | default:"暂无标题" }}</h1>
<p>{{ archive.Description | default:"该文章暂无简介，敬请期待。" }}</p>
<img src="{{ archive.Logo | default:"/static/images/default_logo.png" }}" alt="{{ archive.Title | default:"默认图片" }}">

In this example, ifarchive.TitleIs empty, the page will display "No title available"; ifarchive.DescriptionThe article has no introduction yet, please wait.archive.LogoA default image path will be used if it is empty.

2.default_if_noneFilter

default_if_noneThe filter is more precise, it only applies when the variable is strictly equal tonil（null pointer）when applicable, and will not affect empty strings, empty lists, and other non-nil handle null values. This is very useful in certain scenarios where it is necessary to differentiatenilfrom other empty values.

  • Usage: {{ 变量 | default_if_none:"你的默认值" }}
  • Example:Consider a situation where it may benilThe user objectuser.RealName.
<p>用户姓名：{{ user.RealName | default_if_none:"匿名用户" }}</p>

Ifuser.RealNameYesnil, it will display "Anonymous User"; but ifuser.RealNameis an empty string"",default_if_nonewill not trigger, the page will display an empty string. If you want to handle an empty string, you still need to usedefaultFilter.

Method two: cleverly useif/elseLogical judgment label, implementing more complex default logic

When the setting of the default value requires more complex logical judgment, or the default value itself needs to be dynamically generated based on other conditions, AnQiCMS is powerful.if/elseThe logic judgment label comes into play. It provides a finer control granularity.

  • Usage: 
    
{% if 变量 %}
    {{ 变量 }}
{% else %}
    你的默认值
{% endif %}
  • Example:If the article does not have a thumbnail, and there is an image in the content, automatically extract the first image as the default image; otherwise, display a generic placeholder.
{% if archive.Thumb %}
    <img src="{{ archive.Thumb }}" alt="{{ archive.Title | default:"文章标题" }}">
{% elif archive.ContentImages %} {# 假设存在一个字段 archive.ContentImages 存储内容中的所有图片 #}
    <img src="{{ archive.ContentImages | first }}" alt="{{ archive.Title | default:"文章标题" }}">
{% else %}
    <img src="/static/images/no_image.png" alt="暂无图片">
{% endif %}

This method may be a bit longer than the filter, but its advantage lies in being able to handle multi-level judgment logic, and even call other tags or perform more complex calculations in blocks.elseBlocks can call other tags or perform more complex calculations.

Method three:配合setorwithTag preset variables, improve template maintainability

In certain scenarios, a variable that may be empty is referenced multiple times in a template, and each reference requires the same default value logic. At this time, we can utilizesetorwithLabel the processed variable (including the default value) to a new variable and then refer to this new variable multiple times. This can effectively avoid code repetition and improve the maintainability of the template.

  • setTags:Define a variable within the current scope.

  • withTags:Define a variable within a block scope, usually used to pass variables toincludeLabel.

  • Example:Assumearchive.SeoTitleMay be empty, we want to set a default value for it, and this value is used in<head>and<h1>the label. It will be used in

{# 使用 set 标签预设变量 #}
{% set pageTitle = archive.SeoTitle | default:archive.Title | default:"网站通用标题" %}

<head>
    <title>{{ pageTitle }}</title>
    <meta name="description" content="{{ archive.Description | default:"网站通用描述" }}">
</head>
<body>
    <h1>{{ pageTitle }}</h1>
    {# 页面其他地方也直接使用 pageTitle #}
</body>

Here, we usesetthe label at one time forpageTitledetermining the final display value. Ifarchive.SeoTitleNot empty, use it; otherwise, try usingarchive.Title; ifarchive.TitleAlso empty, use "General Title of the Website". This way, you only need to refer to it in the template laterpageTitleIt is clear in logic and avoids repetition.

Combine content model to set default backend value (auxiliary strategy)

In addition to setting default values at the template level, we can also set default values for custom fields directly in the AnQiCMS content model (configured through "Content Management" -> "Content Model").This is an auxiliary strategy that solves the 'null value' problem at the data source level.

In the setting of custom fields,