将脚本从mysql转换为mysqli

Question

我想将以下脚本从mysql转换为mysqli，但遇到问题。

这是原单脚本用mysql：

//database connection 
    $dbname = 'nursery'; 
    $link = mysql_connect("localhost","root","") or die("Couldn't make connection."); 
    $db = mysql_select_db($dbname, $link) or die("Couldn't select database"); 
    ?> 
    <div style="width:728px;margin:auto;"> 
     <div id='cssmenu'> 
      <ul> 
    <?php 
    function query($parentid) { //function to run a query 
     $query = mysql_query ("SELECT * FROM menu WHERE parentid=$parentid"); 
     return $query; 
    } 
    function has_child($query) { //This function checks if the menus has childs or not 
     $rows = mysql_num_rows ($query); 
     if ($rows > 0) { 
      return true; 
     } else { 
      return false; 
     } 
    } 
    function fetch_menu($query) { 
     while ($result = mysql_fetch_array ($query)) { 
      $menu_id = $result ['id']; 
      $title = $result ['title']; 
      $url = $result ['url']; 
      echo "<li class='has-sub '><a href='{$url}'><span>{$title}</span></a>"; 
      if (has_child (query ($menu_id))) { 
       echo "<ul>"; 
       fetch_menu (query ($menu_id)); 
       echo "</ul>"; 
      } 
      echo "</li>"; 
     } 
    } 
    fetch_menu (query(0)); //call this function with 0 parent id 
    ?> 
      </ul> 
     </div> 
     </div> 

所以我试图将其转换成我的网站的其余部分使用和到目前为止，这已经得到的mysqli：

<?php 
    require("../login/common.php"); 
    //database connection; 
    include '../connect.php'; 
    ?> 
    <div style="width:728px;margin:auto;"> 
     <div id='cssmenu'> 
      <ul> 
    <?php 
    function query($parentid) { //function to run a query 
     $query = mysqli_query ($db, "SELECT * FROM menu WHERE parentid=$parentid"); 
     return $query; 
    } 
    function has_child($query) { //This function checks if the menus has childs or not 
     $rows = mysqli_num_rows ($query); 
     if ($rows > 0) { 
      return true; 
     } else { 
      return false; 
     } 
    } 
    function fetch_menu($query) { 
     while ($result = mysqli_fetch_array ($query)) { 
      $menu_id = $result ['id']; 
      $title = $result ['title']; 
      $url = $result ['url']; 
      echo "<li class='has-sub '><a href='{$url}'><span>{$title}</span></a>"; 
      if (has_child (query ($menu_id))) { 
       echo "<ul>"; 
       fetch_menu (query ($menu_id)); 
       echo "</ul>"; 
      } 
      echo "</li>"; 
     } 
    } 
    fetch_menu (query(0)); //call this function with 0 parent id 
    ?> 
      </ul> 
     </div> 
     </div> 

问题是我得到各种错误，我不完全确定为什么，我知道数据库错误可能下降到$ db没有被传递到函数，但即使我写函数fetch_menu（$查询，$ db）{我仍然有同样的错误？

Notice: Undefined variable: db in   C:\easyphpserver\data\localweb\projects\nursery\menu\menu3.php on line 147 

    Warning: mysqli_query() expects parameter 1 to be mysqli, null given in C:\easyphpserver\data\localweb\projects\nursery\menu\menu3.php on line 147 

    Warning: mysqli_fetch_array() expects parameter 1 to be mysqli_result, null given in  C:\easyphpserver\data\localweb\projects\nursery\menu\menu3.php on line 159 

connect.php的内容是：

<?php 
$db = new mysqli('localhost', 'root', '', 'nursery'); 
$db->set_charset('utf8mb4'); 
    if($db->connect_errno > 0){ 
die('Unable to connect to database [' . $db->connect_error . ']'); 
} 
?> 

Answer 1

通$db到query()

function query($parentid, $db) { 
    $query = mysqli_query ($db, "SELECT * FROM menu WHERE parentid=$parentid"); 
    return $query; 
} 

Answer 2

好了，这个解决方案似乎工作，通过将函数内部的数据库连接，问题是如果我通过键入函数查询（$ parentid，$ db）将$ db包含在函数中，这不起作用并导致错误，但是如果我把db连接放在它工作的函数里.....很奇怪。

<?php 
    //error_reporting(0); 
    require("../login/common.php"); 
    //database connection; 
    include '../connect.php'; 
    ?> 
    <div style="width:728px;margin:auto;"> 
     <div id='cssmenu'> 
      <ul> 
    <?php 
    function query($parentid) { 
     $db = new mysqli('localhost', 'root', '', 'nursery'); 
    $db->set_charset('utf8mb4'); 
    if($db->connect_errno > 0){ 
     die('Unable to connect to database [' . $db->connect_error . ']'); 
    } 
     //function to run a query 
     $query = mysqli_query ($db, "SELECT * FROM menu WHERE parentid=$parentid"); 
     return $query; 
    } 
    function has_child($query) { //This function checks if the menus has childs or not 
     $rows = mysqli_num_rows ($query); 
     if ($rows > 0) { 
      return true; 
     } else { 
      return false; 
     } 
    } 
    function fetch_menu($query) { 
     while ($result = mysqli_fetch_array ($query)) { 
      $menu_id = $result ['id']; 
      $title = $result ['title']; 
      $url = $result ['url']; 
      echo "<li class='has-sub '><a href='{$url}'><span>{$title}</span></a>"; 
      if (has_child (query ($menu_id))) { 
       echo "<ul>"; 
       fetch_menu (query ($menu_id)); 
       echo "</ul>"; 
      } 
      echo "</li>"; 
     } 
    } 
    fetch_menu (query(0)); //call this function with 0 parent id 
    ?> 
      </ul> 
     </div> 
     </div>