The `index` filter returns the index position or other identifier when searching for a specific value in an array?

In Anqi CMS template development, mastering various filters can make the display of page content more flexible and efficient. Among them,indexThe filter is a commonly used tool for handling array or string search tasks. However, many users may have a question when first encountering it: when searching for a specific value in an array,indexThe filter returns whether it is the index position of this value or some other identifier?

The answer is clear: Anqi CMS.indexThe filter returns the value when searching for a specific value in an array or stringThe index position of the first occurrence of a numberIf the value being searched for does not exist, it will return-1This behavior is similar to the search functions of many programming languages, which provide a straightforward numerical value to represent the position of the element.

Deep understandingindexFilter

indexThe filter is mainly used to determine whether the target (string or array/slice) contains a specific keyword and to provide its position information.The principle of its operation is to find the first occurrence of the keyword.

1. Search ObjectIt can be used with strings (to find substrings) and arrays/slices (to find elements).
2. Return value:
   • If the keyword is found, it returns a non-negative integer representing the keywordFirst occurrenceThe starting index position. The index is from0the calculation starts.
   • If the keyword is not found, return-1.
3. Special circumstances:
   • When searching in a string, if the string containsChineseA Chinese character is considered to occupy a position in the calculation3 positionsThis usually has to do with the byte length of UTF-8 encoding.This needs to be paid special attention to when used, as it may be different from the intuitive feeling of 'one character occupies one position' that we are accustomed to.

indexHow to use the filter

indexThe syntax of the filter is very concise:

{{ obj|index:关键词 }}

Here:

• objis the target you want to search for, it can be a string variable, or an array (or slice) variable.
• 关键词in which you want to searchobjthe specific content you want to find.

Actual application example

We will look at several examples in detail.indexHow does the filter work.

Example 1: Searching in a string.

Suppose we have a string.message = "欢迎使用安企CMS（AnQiCMS）".

{% set message = "欢迎使用安企CMS（AnQiCMS）" %}

<div>查找“CMS”的位置：{{ message|index:"CMS" }}</div>
<div>查找“欢迎”的位置：{{ message|index:"欢迎" }}</div>
<div>查找“世界”的位置：{{ message|index:"世界" }}</div>
<div>查找“安企”的位置（注意中文长度）：{{ message|index:"安企" }}</div>

The result will be:

查找“CMS”的位置：18
查找“欢迎”的位置：0
查找“世界”的位置：-1
查找“安企”的位置（注意中文长度）：0

Here, 'welcome' takes up the 0-5 byte positions, and 'anqi' also takes up the 0-5 byte positions, so the index of 'anqi' is still 0.The index of the first 'C' is 18 because the six Chinese characters '欢迎使用安企' occupy 18 bytes in length (6 characters * 3 bytes/character).

Example 2: Searching in an array.

Now we create a string array and find elements within it. We can usesplita filter to split a string into an array by delimiter.

{% set features = "安企CMS,AnQiCMS,内容管理系统,免费建站系统,免费模板"|split:"," %}

<div>在数组中查找“内容管理系统”的位置：{{ features|index:"内容管理系统" }}</div>
<div>在数组中查找“高级SEO”的位置：{{ features|index:"高级SEO" }}</div>

{% set searchKeyword = "免费模板" %}
<div>在数组中查找“{{ searchKeyword }}”的位置：{{ features|index:searchKeyword }}</div>

The result will be:

在数组中查找“内容管理系统”的位置：2
在数组中查找“高级SEO”的位置：-1
在数组中查找“免费模板”的位置：4

when searching within an array,indexThe filter performs an exact match and does not consider substrings as string search does.For example, if you search for "management", it cannot be found in an array containing "Content Management System" because it is not an independent element.

Example three: combining conditional judgment using

indexThe filter returns a numerical result, especially suitable forifcombining with logical judgment tags to achieve more complex template logic.

{% set userRole = ["admin", "editor", "viewer"] %}
{% set currentUser = "editor" %}

{% if userRole|index:currentUser != -1 %}
    <p>当前用户 "{{ currentUser }}" 拥有 "{{ currentUser }}" 角色。</p>
{% else %}
    <p>当前用户 "{{ currentUser }}" 没有找到相应的角色。</p>
{% endif %}

{% set guestUser = "guest" %}
{% if userRole|index:guestUser != -1 %}
    <p>当前用户 "{{ guestUser }}" 拥有 "{{ guestUser }}" 角色。</p>
{% else %}
    <p>当前用户 "{{ guestUser }}" 没有找到相应的角色。</p>
{% endif %}

The result will be:

<p>当前用户 "editor" 拥有 "editor" 角色。</p>
<p>当前用户 "guest" 没有找到相应的角色。</p>

By checkingindexWhether the result of the filter is not equal-1We can easily determine whether a value exists in the target and render different content blocks accordingly.

Summary

Of Security CMSindexA filter is a feature that is intuitive and practical, used to find the numeric index position of the first occurrence of a specific value in a string or array, and return it if not found-1. Understanding its working principle, especially the counting rules of Chinese in string search, can help us build template logic more accurately, thus efficiently managing and displaying website content.

Frequently Asked Questions (FAQ)

How to determine if a value exists in an array or string without concerning the specific position?

If you only need to determine whether a value exists without knowing its specific location, you can usecontainfilter.containThe filter directly returns a boolean value (TrueorFalseDoes it include this value, which is more concise and clear when only an existence check is needed.

2.indexCan the filter find subarrays or patterns (regular expressions) within a string?

indexThe filter performs direct value or substring matching and does not support searching within subarrays.For strings, it only searches for exact substrings and does not support regular expression pattern matching.If a more complex pattern matching is required, it may be necessary to consider processing in the business logic layer and passing the processed data to the template.

3. What if I need to get the index positions of all matches?indexCan the filter do that?

indexThe filter only returns keywordsFirst occurrencethe index position. It cannot directly obtain the index positions of all matching items.To implement this feature, you may need to perform more complex logic processing in Go language code outside the template, or preprocess the data into a structure containing all indices before passing it to the template.On the template level, it focuses on the efficiency and conciseness of the first search.