PHP implementation of infinite Polar classification

Use two for loops to implement an infinite class classification

Table:

Field name	field Type	Notes	Default Value
Id	Int	Primary KEY Auto-increment
Name	varchar	Category name
Pid	Int	Parent class ID	0

the PID of the top level classification is 0 by default . When we want to take out a subcategory of a classification tree, the basic idea is recursion , of course, for efficiency issues do not recommend each recursive query database , the usual practice is to remove all the categories, the data stored in the PHP array, and then processed , you can finally cache the results to increase the efficiency of the next request.

First, build an original array , which is queried directly from the database:

1. Building Data

$categories = array(
    array('id'=>1,'name'=>'电脑','pid'=>0),
    array('id'=>2,'name'=>'手机','pid'=>0),
    array('id'=>3,'name'=>'笔记本','pid'=>1),
    array('id'=>4,'name'=>'台式机','pid'=>1),
    array('id'=>5,'name'=>'智能机','pid'=>2),
    array('id'=>6,'name'=>'功能机','pid'=>2),
    array('id'=>7,'name'=>'超级本','pid'=>3),
    array('id'=>8,'name'=>'游戏本','pid'=>3),
);

The goal is to convert it into the following structure
Computers > Notebooks >> Super Ben >> game ben > Desktop
Mobile > Smart machine > Function Machine

With an array, you can add a children key to store its subcategories :

array(
    //1对应$categories中的id ，方便直接读取
    1 => array(
        'id'=>1,
        'name'=>'电脑',
        'pid'=>0,
        children=>array(
            &array(
                'id'=>3,
                'name'=>'笔记本',
                'pid'=>1,
                'children'=>array(
                    //此处省略
                )
            ),
            &array(
                'id'=>4,
                'name'=>'台式机',
                'pid'=>1,
                'children'=>array(
                    //此处省略
                )
            ),
        )
    ),
    //其他分类省略
)

2. Processing process:

$tree = array();
//第一步，将所有的分类id作为数组key,并创建children单元
foreach($categories as $category){
    $tree[$category['id']] = $category;
    $tree[$category['id']]['children'] = 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['pid'] != 0) {
        $tree[$value['pid']]['children'][] = &$tree[$key];
    }
}
print_r($tree);

注:必须通过引用, 否则不会一次遍历就生成最终的结果.

3. The printed results are as follows:

Array ([1] => array ([ID] => 1 [name] => computer [PID] => 0
                            [Children] => Array ([0] => Array (
                            [ID] => 3 [name] => notebook [pid] => 1 [Children] => Array ([0] =&G T
                                            Array ([id] => 7
                                            [Name] => super [PID] => 3
                                                [Children] => Array (
                        )) [1] => Array                ([ID] => 8 [NA Me] => game [PID] => 3 [child
                                        Ren] => Array () )) [1] = 
                            > Array ([id] => 4 [name] => desktop
                                [PID] => 1 [children] => Array
        ())) [2] => Array
                ([id] => 2 [name] => mobile [PID] => 0 [children] => Array
            (        [0] => Array ([id] => 5 [NA
                                Me] => smart machine [PID] => 2 [children] => Array
                        ()) [1] => Array
                            ([ID] => 6 [name] => function machine
                                [PID] => 2 [children] => Array (  )) [3] => Array ([id]
                    => 3 [name] => notebook [pid] => 1 [children] => Array (
                            [0] => Array ([id] => 7
   [Name] => super Ben                         [PID] => 3 [children] => Array
                        ()) [1] => Array ([ID] => 8 [name] => game [PID]
                                => 3 [Children] => Array (
            ))) [4] => Array ([id] => 4
        [Name] => desktop [PID] => 1 [children] => Array ()
            ) [5] => Array ([id] => 5 [name] => smart machine [PID] => 2 [Children] => Array ()) [6] => array ([ID] => 6 [NamE] => function machine [PID] => 2 [children] => Array ()) [7] => Array ([id] => 7 [name] => super [PID] => 3 [C
            Hildren] => Array ()) [8] => array ([ID] => 8
                [Name] => game [PID] => 3 [children] => Array ( )
        )
)

Advantages: Clear relationship, modify the relationship between the superior and subordinate is simple.

Disadvantages: use PHP processing, if the number of large categories, efficiency will also be reduced.