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PHP implements infinite classification_PHP tutorial

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Release： 2016-07-13 09:45:55

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PHP implements infinite classification

Use two for loops to achieve infinite classification

Table:

字段名	字段类型	备注	默认值
id	int	主键 auto-increment
name	varchar	分类名称
pid	int	父类id	0

The default pid of the top category is 0. When we want to take out the sub-category tree of a certain category, the basic idea is recursion . Of course, due to efficiency issues it is not recommended to query the database for every recursion. The usual approach is First take out all categories, save the data into a PHP array, and then process . Finally, you can cache the results to improve the efficiency of the next request.

First let's build an original array , which can be queried directly from the database:

1. Construct data

<code class="hljs php">$categories = array(
    array(&#39;id&#39;=>1,&#39;name&#39;=>&#39;电脑&#39;,&#39;pid&#39;=>0),
    array(&#39;id&#39;=>2,&#39;name&#39;=>&#39;手机&#39;,&#39;pid&#39;=>0),
    array(&#39;id&#39;=>3,&#39;name&#39;=>&#39;笔记本&#39;,&#39;pid&#39;=>1),
    array(&#39;id&#39;=>4,&#39;name&#39;=>&#39;台式机&#39;,&#39;pid&#39;=>1),
    array(&#39;id&#39;=>5,&#39;name&#39;=>&#39;智能机&#39;,&#39;pid&#39;=>2),
    array(&#39;id&#39;=>6,&#39;name&#39;=>&#39;功能机&#39;,&#39;pid&#39;=>2),
    array(&#39;id&#39;=>7,&#39;name&#39;=>&#39;超级本&#39;,&#39;pid&#39;=>3),
    array(&#39;id&#39;=>8,&#39;name&#39;=>&#39;游戏本&#39;,&#39;pid&#39;=>3),
);</code>

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The goal is to convert it into the following structure
Computers >Notebooks >>Ultrabooks >> Gaming notebooks > Desktops
Mobile phones > Smartphones > Function phones

If represented by an array, you can add a children key to store its subcategories :

<code class="hljs php">array(
    //1对应$categories中的id ，方便直接读取
    1 => array(
        &#39;id&#39;=>1,
        &#39;name&#39;=>&#39;电脑&#39;,
        &#39;pid&#39;=>0,
        children=>array(
            &array(
                &#39;id&#39;=>3,
                &#39;name&#39;=>&#39;笔记本&#39;,
                &#39;pid&#39;=>1,
                &#39;children&#39;=>array(
                    //此处省略
                )
            ),
            &array(
                &#39;id&#39;=>4,
                &#39;name&#39;=>&#39;台式机&#39;,
                &#39;pid&#39;=>1,
                &#39;children&#39;=>array(
                    //此处省略
                )
            ),
        )
    ),
    //其他分类省略
)</code>

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2. Processing process:

<code class="hljs php">$tree = array();
//第一步，将所有的分类id作为数组key,并创建children单元
foreach($categories as $category){
    $tree[$category[&#39;id&#39;]] = $category;
    $tree[$category[&#39;id&#39;]][&#39;children&#39;] = array();
}
//第二步，利用引用，将每个分类添加到父类children数组中，这样一次遍历即可形成树形结构。
foreach ($tree as $key=>$value) {
    if ($value[&#39;pid&#39;] != 0) {
        $tree[$value[&#39;pid&#39;]][&#39;children&#39;][] = &$tree[$key];
    }
}
print_r($tree);</code>

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<code>注:必须通过引用, 否则不会一次遍历就生成最终的结果.
</code>

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3. The print result is as follows:

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Advantages: The relationship is clear and it is easy to modify the relationship between superiors and subordinates.

Disadvantages: Using PHP processing, if the number of categories is huge, the efficiency will also be reduced.