PHP implements unlimited classification query (recursive, non-recursive), classification query recursion_PHP tutorial

php implements infinite level classification query (recursive, non-recursive), classification query recursion

I have been working in PHP for so long, and I found that an indispensable application module of the backend management system is the column column Classification, generally the columns should be made into infinite levels, which means that each column can theoretically add sub-columns. In my opinion, handling this situation is not very complicated overall. The only relatively difficult point is the query of infinite columns.

Let me give you a brief introduction to this situation. There are generally two ways to query this kind of infinite column. One of them is to use the stack mechanism, and the other is to use a recursive function. way (of course the recursive function implementation mechanism is also implemented with the help of the stack). We will introduce these two methods separately below.

Recursive function implementation

As mentioned above, recursive functions are also implemented with the help of the stack mechanism, but the underlying stack processing is transparent to programmers, who only need to care about the implementation logic of the application. Therefore, it is easier to understand using recursion to deal with the above problems, and the code is relatively concise.

Since a recursive function is used, we know from the name that we must use a custom function. Let me first briefly talk about its implementation ideas, and we will reflect the specific details in the code.

The main job of each layer's function is to find the column whose parent ID is the current ID. After finding it, call its own function again and use the found column's ID as the parent ID of the next layer.

The flow chart is as follows

Picture 1

I don’t know if you can understand the above explanation. It doesn’t matter. Let’s just look at the code below

<?php
/**
 * 个人博客：迹忆博客
 * 博客地址：www.onmpw.com
 * 递归实现无限极分类
 */
$channels = array(
  array('id'=>1,'name'=>"衣服",'parId'=>0),
  array('id'=>2,'name'=>"书籍",'parId'=>0),
  array('id'=>3,'name'=>"T恤",'parId'=>1),
  array('id'=>4,'name'=>"裤子",'parId'=>1),
  array('id'=>5,'name'=>"鞋子",'parId'=>1),
  array('id'=>6,'name'=>"皮鞋",'parId'=>5),
  array('id'=>7,'name'=>"运动鞋",'parId'=>5),
  array('id'=>8,'name'=>"耐克",'parId'=>7),
  array('id'=>9,'name'=>"耐克",'parId'=>3),
  array('id'=>10,'name'=>"鸿星尔克",'parId'=>7),
  array('id'=>11,'name'=>"小说",'parId'=>2),
  array('id'=>12,'name'=>"科幻小说",'parId'=>11),
  array('id'=>13,'name'=>"古典名著",'parId'=>11),
  array('id'=>14,'name'=>"文学",'parId'=>2),
  array('id'=>15,'name'=>"四书五经",'parId'=>14)
);
$html = array();
/**
 * 递归查找父id为$parid的结点
 * @param array $html  按照父-》子的结构存放查找出来的结点
 * @param int $parid  指定的父id
 * @param array $channels  数据数组
 * @param int $dep  遍历的深度，初始化为1
 */
function getChild(&$html,$parid,$channels,$dep){
  /*
   * 遍历数据，查找parId为参数$parid指定的id
   */
  for($i = 0;$i<count($channels);$i++){
    if($channels[$i]['parId'] == $parid){
      $html[] = array('id'=>$channels[$i]['id'],'name'=>$channels[$i]['name'],'dep'=>$dep);
      getChild($html,$channels[$i]['id'],$channels,$dep+1);
    }
  }
}
getChild($html,0,$channels,1);
?>

This is the core code for recursively implementing infinite column query. You should have a clearer understanding of its implementation process based on Figure 1.

Non-recursive, that is, using the stack mechanism to realize infinite column query

Above we briefly introduced the use of recursion to query infinite columns. Below we briefly introduce the non-recursive method. Although recursive functions are not used, in view of the structure page of infinite columns, it is necessary to refer to the recursive implementation mechanism-the stack mechanism to solve this problem.

When I was in school, my teacher said that the core mechanism of a stack is actually just four words: first in, last out.

I won’t talk much about the mechanism of the stack here, but I will mainly talk about how to use the stack to implement unlimited column queries.

1. First push the top column into the stack

2. Pop the top element from the stack

3. Store the popped element into the array and mark its depth (the depth is to add 1 to the depth of its parent column)

4. Use the popped element as the parent column and find its sub-column

5. Push the found sub-column into the stack and repeat step 2

6. If the stack is judged to be empty, the process ends;

By translating the above steps, these steps can be translated into PHP code. The core code is as follows

<?php
/**
 * 个人博客：迹忆博客
 * 博客地址：www.onmpw.com
*使用非递归，即使用栈的方式实现栏目的无限极分类查询
*/
$channels = array(
  array('id'=>1,'name'=>"衣服",'parId'=>0),
  array('id'=>2,'name'=>"书籍",'parId'=>0),
  array('id'=>3,'name'=>"T恤",'parId'=>1),
  array('id'=>4,'name'=>"裤子",'parId'=>1),
  array('id'=>5,'name'=>"鞋子",'parId'=>1),
  array('id'=>6,'name'=>"皮鞋",'parId'=>5),
  array('id'=>7,'name'=>"运动鞋",'parId'=>5),
  array('id'=>8,'name'=>"耐克",'parId'=>7),
  array('id'=>9,'name'=>"耐克",'parId'=>3),
  array('id'=>10,'name'=>"鸿星尔克",'parId'=>7),
  array('id'=>11,'name'=>"小说",'parId'=>2),
  array('id'=>12,'name'=>"科幻小说",'parId'=>11),
  array('id'=>13,'name'=>"古典名著",'parId'=>11),
  array('id'=>14,'name'=>"文学",'parId'=>2),
  array('id'=>15,'name'=>"四书五经",'parId'=>14)
);
$stack = array(); //定义一个空栈
$html = array();  //用来保存各个栏目之间的关系以及该栏目的深度
/*
 * 自定义入栈函数
 */
function pushStack(&$stack,$channel,$dep){
  array_push($stack, array('channel'=>$channel,'dep'=>$dep));
}
/*
 * 自定义出栈函数
 */
function popStack(&$stack){
  return array_pop($stack);
}
/*
 * 首先将顶级栏目压入栈中
 */
foreach($channels as $key=>$val){
  if($val['parId'] == 0)
    pushStack($stack,$val,0);
}
/*
 * 将栈中的元素出栈，查找其子栏目
 */
do{
  $par = popStack($stack); //将栈顶元素出栈
  /*
   * 查找以此栏目为父级栏目的id，将这些栏目入栈
   */
  for($i=0;$i<count($channels);$i++){
    if($channels[$i]['parId'] == $par['channel']['id']){
      pushStack($stack,$channels[$i],$par['dep']+1);
    }
  }
  /*
   * 将出栈的栏目以及该栏目的深度保存到数组中
   */
  $html[] = array('id'=>$par['channel']['id'],'name'=>$par['channel']['name'],'dep'=>$par['dep']);
}while(count($stack)>0);

The above is implemented using a non-recursive method.

Download code: https://github.com/onmpw/phpApp

Summary

The above two methods have their own advantages and disadvantages. Although the implementation forms are different, in view of the structure of the infinite column, the implementation mechanism of both is the same - both are implemented with the help of stack. In real situations, we have to choose a way to implement it based on the needs of the real situation.

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