PHP makes it easy to perform unlimited queries

PHP is a widely used open source scripting language and is a very important part of website development. In many website development, unlimited classification structure is a very common requirement. This article will introduce how to use PHP to easily perform unlimited queries.

1. What is infinite classification?

Infinite classification is a tree-structured classification method, which is very common in websites. For example, in a product classification website, if you need to classify products, you can use unlimited classification. We can arrange products at unlimited levels according to large categories, small categories, sub-categories, etc.

2. How to implement infinite classification?

1. Use recursive method to achieve

In PHP, we can use recursive method to implement infinite classification query. The specific implementation method is as follows:

<?php

function getSubCates($cateList, $parentId = 0, $level = 0) {
    $subs = array();     // 子分类列表
    foreach ($cateList as $cate) {
        if ($cate[&#39;parent_id&#39;] == $parentId) {
            $cate[&#39;level&#39;] = $level;    // 设置当前分类的级别
            $subs[] = $cate;
            $subs = array_merge($subs, getSubCates($cateList, $cate[&#39;id&#39;], $level + 1));
        }
    }
    return $subs;
}

In the above code, the subcategories of a category are queried, and then the subcategories of each subcategory are queried recursively, and all categories are returned in an array hierarchically.

2. Use the stack method to achieve

In addition to using the recursive method, you can also use the stack method to achieve infinite classification. The code for stack mode is as follows:

<?php

function getSubCates($cateList, $rootId = 0) {
    $stack = array($rootId);
    $subs = array();
    while (!empty($stack)) {
        $parentId = array_pop($stack);
        foreach ($cateList as $key => $row) {
            if ($row['parent_id'] == $parentId) {
                $subs[] = $row;
                array_push($stack, $row['id']);
                unset($cateList[$key]);
            }
        }
    }
    return $subs;
}

The above code uses the stack data structure, puts the root node into the stack, loops out the parent node from the stack and finds its child nodes, and at the same time pushes the child node into the stack. , until the stack is empty.

3. How to use infinite classification?

Using unlimited classification can greatly facilitate our development. Categories can be arranged into a neat tree structure, making it easier for users to browse and find targets. The following is a commonly used example:

<?php

$cateList = array(
    array(&#39;id&#39; => 1, 'name' => '电子产品', 'parent_id' => 0),
    array('id' => 2, 'name' => '手机', 'parent_id' => 1),
    array('id' => 3, 'name' => '笔记本电脑', 'parent_id' => 1),
    array('id' => 4, 'name' => '三星', 'parent_id' => 2),
    array('id' => 5, 'name' => '华为', 'parent_id' => 2),
    array('id' => 6, 'name' => 'ThinkPad', 'parent_id' => 3),
    array('id' => 7, 'name' => 'Apple', 'parent_id' => 3),
);

$subCates = getSubCates($cateList);
foreach ($subCates as $cate) {
    echo str_repeat('  ', $cate['level']) . $cate['name'];
    echo '<br/>';
}

In the above code, we first define a category list $cateList, then call the getSubCates($cateList) method to obtain all categories, and finally use a loop to output the information of each category name and level.

4. Summary

Infinite classification is an important classification method and is very practical. In PHP, we can use recursion or stack to easily implement unlimited queries. Unlimited classification can help us quickly build a tree structure to facilitate user query and browsing. I hope the above introduction can help readers better understand the method of implementing unlimited queries in PHP.

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