In managing and displaying content in the Anqi CMS, the flexibility of the template is the key to improving website operational efficiency.The built-in Django template engine syntax provides a variety of practical filters, allowing us to handle various data in a concise and efficient manner.sliceIt can help us accurately extract a specific part of the array (or called slice in Go language environment), especially how to get all elements except the first and last one.

The display of content is the core of website operation, whether it is article list, product display or image gallery, we often need to control the data finely.Sometimes, in order to layout or highlight the key points, we may need to treat the first and last elements of the list specially, while displaying the middle part uniformly.sliceThe filter can be put to good use.

UnderstandingsliceThe filter: a powerful tool for data truncation.

In the template system of AnQi CMS,sliceFilter is a very powerful tool that allows us to perform flexible extraction operations on strings or arrays. Its basic syntax is{{ obj|slice:"from:to" }}where:

  • objis the string or array variable you want to extract.
  • fromSpecify the starting position for extraction (including the element at this position). If not setfromit defaults to the first element (index 0).
  • toSpecify the end position of the substring (elements after this position are not included). If not setto, the default is to take the last element.

Here the numerical index starts from 0, which means the index of the first element in the array is 0, the second is 1, and so on. IftoThe parameter is negative, it will start counting from the end of the array. For example,-1Represents the last element,-2Represents the second-to-last element.

Let's feel its usage through several simple examples:

  • {{ "abcdefg"|slice:":3" }}It will cut the first 3 characters of the string, outputabc.
  • {{ ["A", "B", "C", "D", "E"]|slice:"1:3"|join:", " }}The elements from index 1 to index 2 of the array will be extracted and outputB, C.
  • {{ ["A", "B", "C", "D", "E"]|slice:"2:"|join:", " }}Elements from index 2 to the end of the array will be extracted and outputC, D, E.

ingeniously utilizeslice: Get all elements except the first and last

Now, let's solve the core issue: how to get all elements of an array except the first and last?

This requirement can be met by setting upfromandtoparameters.

  1. Skip the first element： To exclude the first element of the array, we just need to let the slice start from index1。所以，fromparameter settings1.

  2. Skip the last element： To exclude the last element of the array, we need to end the slicing before the last element.slicein the filter, totoparameter settings-1This means to cut off to the second last element, thereby naturally excluding the last one.

Combining these two, we getslice:"1:-1"this exquisite combination.

Let's look at a practical example. Suppose we have a list of articles and we want to display all articles on the page except the first and the last one:

{# 假设这是我们通过 archiveList 标签获取的文档列表，这里为了演示方便直接定义数组 #}
{% set all_articles = ["安企CMS入门指南", "网站内容营销策略", "Go语言开发实践", "SEO优化核心技巧", "多站点管理进阶"] %}

<h3>所有文章列表：</h3>
<ul>
    {% for article in all_articles %}
        <li>{{ article }}</li>
    {% endfor %}
</ul>

<h3>获取除首尾外的中间文章：</h3>
<ul>
    {% set middle_articles = all_articles|slice:"1:-1" %}
    {# 使用 if 条件判断，确保数组中有足够的元素才进行遍历 #}
    {% if middle_articles %}
        {% for article in middle_articles %}
            <li>{{ article }}</li>
        {% endfor %}
    {% else %}
        <li>当前列表元素不足，无法获取中间内容。</li>
    {% endif %}
</ul>

In the above example,all_articlesContaining 5 articles. After|slice:"1:-1"Filtered,middle_articlesIt will only include"网站内容营销策略","Go语言开发实践","SEO优化核心技巧"these three articles.

Application scenarios and robustness considerations

This truncation method is very useful in many practical scenarios. For example:

  • Image Gallery: If your website has a picture carousel, the first and last pictures should have special navigation or display styles, while the middle pictures need to be displayed uniformly.
  • Related ArticlesIn displaying related article lists, you may want to exclude the current article itself and another specially recommended article.
  • Complex navigation：Build complex navigation menus may require special layout requirements for the first and last elements, while the middle links use a regular style.

It is worth noting that when the length of the original array is not sufficient to meetslicethe requirements of the filter, for example, when the array has only 0, 1, or 2 elements,slice:"1:-1"It will return an empty array. In the above example, we added{% if middle_articles %}Determine, it is a good habit, which can ensure that there will be no unexpected blank or error information on the page when there are no intermediate elements, thereby enhancing the robustness of the template.

PasssliceFilter, template developers of AnQi CMS can finely control the display of content, easily achieve various complex data slicing logic, making the layout of your website content more flexible and accurate.

Common Questions (FAQ)

1.sliceFilter can be used for what types of data?

sliceThe filter is mainly used to process strings and arrays (also known as slices in Go language). You can use it to extract substrings of strings or get partial elements from arrays.

2. If the number of elements in the original array is very small, such as only two elements,slice:"1:-1"what will it return?

When the number of elements in the array is not enough to meet the cutting range,sliceThe filter will return an empty array. For example, an array with only two elements.["A", "B"]Use|slice:"1:-1"will result in an empty array becausefrom=1it skipped “A” insteadto=-1The request to end before “B” resulted in no elements to take. Therefore, it is recommended to add in the processing result to avoid display issues caused by an empty array.{% if ... %}Judgment to avoid display issues caused by an empty array.

3. Besides getting the middle element,sliceWhat are some common uses of the filter?

sliceThe filter is very flexible, and there are many other uses:

  • Get the first N elements:{{ my_array|slice:":N" }}(For example}]}my_array|slice:":3"Get the first 3).
  • Get the next N elements:{{ my_array|slice:"-N:" }}(For example}]}my_array|slice:"-3:"Get the next 3)
  • From a certain index to the end:{{ my_array|slice:"N:" }}(For example}]}my_array|slice:"2:"From index 2 to the end)
  • Get a specific range:{{ my_array|slice:"N:M" }}(For example}]}my_array|slice:"1:4"Get elements from index 1 to 3). These usages can help you precisely control data display according to specific needs.