我已经在程序上使用PHP多年了，但我决定真正与时俱进，开始练习OOP。
假设我有如下所示的内容：
<?php
$db = new mysqli(host, user, pass, db);
class user {
public $username;
public function __construct($ID) {
$sql_query = "SELECT `username` FROM `users` WHERE `userid`='$ID'";
// execute that query somehow, store result in $result.
$this->username = $result;
}
}
$some_user = new user(1);
（我知道查询需要转义等，我只是想举一个基本的例子）
我的主要问题是与类中的$db对象交互的最佳方式是什么？我会打电话给$db->query($sql_query);但$db无法访问。很多谷歌搜索都没有给我一个可靠的答案，但我看到了很多将$db对象传递到构造函数中的建议，例如：
$some_user = new user(1, $db);
我将其理解为"数据注入"是否正确？似乎必须有比将其显式包含在每个构造函数中更好的方法。当然，我总是可以在每个类中创建$db，但重复连接到数据库似乎也没有必要。
//this seems to happen in the global scope, so $db isn't accessible in class user yet
$db = new mysqli(host, user, pass, db);
class user {
public $username;
//to make global $db accessible, pass a reference to user's constructor:
public function __construct($ID,&$db) {
$sql_query = "SELECT `username` FROM `users` WHERE `userid`='$ID'";
// execute that query somehow, store result in $result
// if you exec the query, first you get a mysqli result *OBJECT*:
$result_obj = $db -> query($sql_query);
// next you pull out the row out of this object as an associative array:
$row = $result_obj -> fetch_assoc();
//finally you assign the retrieved value as a property of your user:
$this->username = $row['username'];
}
}
//be careful NOT to pass a reference here!!
$some_user = new user(1,$db); // NO ampersand here! passing by ref is deprecated!