Some applications of recursion (2) Infinite classification

Use recursive method to achieve infinite classification

Usually when I am writing a project, I will implement the corresponding classification superior classification when writing something such as mall classification, or other projects department management’s superior departmentI will generally use Infinite Classify by extreme classification

Step 1: First of all, when designing the data table, if I want to implement Infinitus classification, I usually add an additional field pid to the data table. Let me explain it through a new data table,

(1) Create table:

----------------------------

-- Table structure for pid

----------------------------

DROP TABLE IF EXISTS `pid`;

CREATE TABLE pid (

id tinyint unsigned NOT NULL AUTO_INCREMENT primary key comment 'primary key id',

name varchar(32) NOT NULL,

nickname varchar(32) DEFAULT NULL,

pid tinyint(10) unsigned DEFAULT NULL,

sort mediumint(10) unsigned DEFAULT 50

) ENGINE=InnoDB DEFAULT CHARSET=utf8;

(2) Insert data:

----------------------------

-- Records of pid

----------------------------

INSERT INTO `pid` VALUES ('1', 'Technology', '', '0', '50');

INSERT INTO `pid` VALUES ('2', 'Military', '', '0', '50');

INSERT INTO `pid` VALUES ('3', 'human and nature', '', '0', '50');

INSERT INTO `pid` VALUES ('4', 'Gourmet', '', '0', '50');

INSERT INTO `pid` VALUES ('5', 'Artificial Intelligence', '', '1', '50');

INSERT INTO `pid` VALUES ('6', 'robot', '', '5', '50');

INSERT INTO `pid` VALUES ('7', 'drone', '', '5', '50');

INSERT INTO `pid` VALUES ('8', 'Autonomous Car', '', '5', '50');

INSERT INTO `pid` VALUES ('9', 'Military robot', 'Haha', '6', '50');

INSERT INTO `pid` VALUES ('10', 'Service Robot', '', '6', '50');

INSERT INTO `pid` VALUES ('11', 'aircraft carrier', '', '2', '50');

INSERT INTO `pid` VALUES ('12', 'carrier-based aircraft', '', '2', '50');

INSERT INTO `pid` VALUES ('13', 'Early Warning Aircraft', '', '2', '50');

INSERT INTO `pid` VALUES ('14', 'missile', '', '2', '50');

INSERT INTO `pid` VALUES ('15', 'A Bite of China', '', '3', '50');

INSERT INTO `pid` VALUES ('16', 'Sichuan cuisine', '', '15', '50');

INSERT INTO `pid` VALUES ('17', 'Cantonese', '', '15', '50');

INSERT INTO `pid` VALUES ('18', 'Hunan cuisine', '', '15', '50');

INSERT INTO `pid` VALUES ('19', 'bio', '', '4', '50');

INSERT INTO `pid` VALUES ('20', 'animal', '', '19', '50');

INSERT INTO `pid` VALUES ('21', 'Plant', '', '19', '50');

INSERT INTO `pid` VALUES ('26', 'Haha', 'Haha', '0', '50');

INSERT INTO `pid` VALUES ('27', 'Hey hey hey', 'Hey hey hey', '26', '50');

INSERT INTO `pid` VALUES ('28', 'Pssssss', 'ssssssss', '26', '50');

Data Sheet:

The data sheet looks like this.

Step 2: Get to the point, Infinitus classification

<?<span style="color: #000000;">php
</span><span style="color: #008000;">//</span><span style="color: #008000;">设置字符集</span>
header(<span style="color: #800000;">'</span><span style="color: #800000;">content-type:text/html;charset=utf-8</span><span style="color: #800000;">'</span><span style="color: #000000;">);

</span><span style="color: #008000;">/*</span><span style="color: #008000;">*
 * 无限极分类
 * @param   $list array()
 * return array
 </span><span style="color: #008000;">*/</span>
<span style="color: #008000;">//</span><span style="color: #008000;">无限极分类，实现具有父子关系的数据分类</span>
function category($arr,$pid=<span style="color: #800080;">0</span>,$level=<span style="color: #800080;">0</span><span style="color: #000000;">){
    </span><span style="color: #008000;">//</span><span style="color: #008000;">定义一个静态变量，存储一个空数组，用静态变量，是因为静态变量不会被销毁，会保存之前保留的值，普通变量在函数结束时，会死亡，生长周期函数开始到函数结束，再次调用重新开始生长
    </span><span style="color: #008000;">//</span><span style="color: #008000;">保存一个空数组</span>
    <span style="color: #0000ff;">static</span> $list=<span style="color: #000000;">array();
    </span><span style="color: #008000;">//</span><span style="color: #008000;">通过遍历查找是否属于顶级父类，pid=0为顶级父类，</span>
    <span style="color: #0000ff;">foreach</span>($arr <span style="color: #0000ff;">as</span><span style="color: #000000;"> $value){
        </span><span style="color: #008000;">//</span><span style="color: #008000;">进行判断如果pid=0，那么为顶级父类，放入定义的空数组里</span>
        <span style="color: #0000ff;">if</span>($value[<span style="color: #800000;">'</span><span style="color: #800000;">pid</span><span style="color: #800000;">'</span>]==<span style="color: #000000;">$pid){
            </span><span style="color: #008000;">//</span><span style="color: #008000;">添加空格进行分层</span>
            $arr[<span style="color: #800000;">'</span><span style="color: #800000;">level</span><span style="color: #800000;">'</span>]=<span style="color: #000000;">$level;
            $list[]</span>=<span style="color: #000000;">$value;
            </span><span style="color: #008000;">//</span><span style="color: #008000;">递归点，调用自身，把顶级父类的主键id作为父类进行再调用循环，空格+1</span>
            category($arr,$value[<span style="color: #800000;">'</span><span style="color: #800000;">id</span><span style="color: #800000;">'</span>],$level+<span style="color: #800080;">1</span><span style="color: #000000;">);
        }
    }
    </span><span style="color: #0000ff;">return</span> $list;<span style="color: #008000;">//</span><span style="color: #008000;">递归出口</span>
}

Connect data:

Effect:

2. A small extension:

This is just my own understanding of the Infinitus classification and some summary of my own knowledge points. If there is something wrong, I hope you can give me some suggestions, learn together, and make progress together. thanks~