函数PHP中的Mysqli连接

Question

我遇到了一个 PHP 问题。我在网上搜索过，但找不到答案。到目前为止，这是我的代码：

<?php
   $db_host = 'db_host';
   $db_user = 'db_user';
   $db_password = 'db_password';
   $db_name = 'db_name';
   //not showing you the real db login ofcourse

   $conn = mysqli_connect($db_host, $db_user, $db_password, $db_name);
   if($conn) {
      echo 'We are connected!';
   }

到这里，一切顺利。连接已建立，“我们已连接！”出现在屏幕上。

function login($username, $password, $conn) {
   $result = $conn->query("SELECT * FROM users");
   echo mysqli_errno($conn) . mysqli_error($conn);
} 

但是，当我运行此函数时，会弹出 mysqli 错误“未选择数据库”。于是我在函数前和函数中的文件中添加了如下代码，所以总的代码变成了：

<?php
   $db_host = 'db_host';
   $db_user = 'db_user';
   $db_password = 'db_password';
   $db_name = 'db_name';
   //not showing you the real db login ofcourse

   $conn = mysqli_connect($db_host, $db_user, $db_password, $db_name);
   if($conn) {
      echo 'We are connected!';
   }

   if (!mysqli_select_db($conn, $db_name)) {
      die("1st time failed");
   }

   function login($username, $password, $conn, $db_name) {
      if (!mysqli_select_db($conn, $db_name)) {
         die("2nd time failed");
      }
      $result = $conn->query("SELECT * FROM users");
      echo mysqli_errno($conn) . mysqli_error($conn);
   } 

   $username = 'test';
   $password = 'test';
   login($username, $password, $conn, $db_name);
?>

第一次添加数据库名称可以正常工作，但是在函数中它不起作用。我也尝试在函数内部使用 global $conn ，但这也不起作用。将 mysqli_connect() 更改为 new mysqli() 也没有任何效果。

提前致谢！

Answer 1

请注意，此代码是根据您的代码重构的，不推荐登录逻辑。请尝试此代码并进行您认为需要的更改。

确保您的数据库信息也根据需要更新。

MyDB 类

Class MyDB {

protected $_DB_HOST = 'localhost';
protected $_DB_USER = 'user';
protected $_DB_PASS = 'password';
protected $_DB_NAME = 'table_name';
protected $_conn;

public function __construct() {
    $this->_conn = mysqli_connect($this->_DB_HOST, $this->_DB_USER, $this->_DB_PASS);
    if($this->_conn) {
        echo 'We are connected!<br>';
    }
}

public function connect() {
    if(!mysqli_select_db($this->_conn, $this->_DB_NAME)) {
        die("1st time failed<br>");
    }

    return $this->_conn;
}

}

登录类

Class Login {

protected $_conn;

public function __construct() {
    $db = new MyDB();
    $this->_conn = $db->connect();
}

//This is a HORRIBLE way to check your login. Please change your logic here. I am just kind of re-using what you got
public function login($username, $password) {
    $result = $this->_conn->query("SELECT * FROM user WHERE username ='$username' AND password='$password'");

    if(!$result) {
        echo mysqli_errno($this->_conn) . mysqli_error($this->_conn);
        return false;
    }

    return $result->fetch_row() > 0;
}

}

用法

$login = new Login();
$logged = $login->login('username', 'password');

if ($logged) {
    echo "yeah!! you are IN";
} else {
    echo "boo!! . Wrong username and password";
}