How to recursively query all child nodes below in PHP

PHP is one of the mainstream languages ​​​​for website development at present. For developers using PHP, recursive query is a very basic but practical function. This article will introduce how to recursively query everything in PHP.

1. What is all under recursive query

Recursion is an effective method to solve problems. Recursive algorithms are widely used in programming, such as search engine crawlers, file system traversal, algorithm problems, etc. All under the recursive query is to start from the specified root node and recursively query all the child nodes below.

2. Code Implementation

In PHP, to recursively query all items, we can use recursive functions. Here we use a simple example to explain all the implementation processes under recursive query.

function display_all($id){
  //根据$id查询出下级分类
  $list = get_child_list($id);
  if(empty($list)){
    return;
  }
  foreach($list as $v){
    echo $v['name'].'<br>';
    //递归调用函数本身
    display_all($v['id']);
  }
}

The most critical thing about the display_all() function in the above code is its own recursive call. In this function, first query the lower-level categories based on $id, then traverse the lower-level categories, and output the names of the lower-level categories. During the traversal process, we call the display_all() function recursively until there are no lower-level categories.

3. Notes

When using all recursive queries, you need to pay attention to the following matters:

1. It is recommended to use recursive depth control to avoid Infinite recursion situation.
2. Ensure that operations performed in recursion do not affect the performance and stability of the entire program.
3. If you use recursive database operation, you need to pay attention to avoid performance problems caused by too many database connection pools.

4. Summary

All under recursive query is a very practical function, especially when processing data with hierarchical relationships, it is indispensable. This article introduces how to implement this function through recursive functions in PHP, and also introduces some issues that need attention. Hope this article is helpful to everyone.

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