php封装mysqli的使用

<?php
class DB {
    private $host = "localhost";
    private $username = "user";
    private $password = "password";
    private $dbname = "database";
    private $conn;

    public function __construct() {
        $this->connect();
    }

    private function connect() {
        $this->conn = new mysqli($this->host, $this->username, $this->password, $this->dbname);
        if ($this->conn->connect_error) {
            die("连接失败: " . $this->conn->connect_error);
        }
    }

    public function query($sql) {
        return $this->conn->query($sql);
    }

    public function escape($string) {
        return $this->conn->real_escape_string($string);
    }

    public function close() {
        $this->conn->close();
    }
}

// 使用示例
$db = new DB();
$result = $db->query("SELECT * FROM users");
while ($row = $result->fetch_assoc()) {
    echo $row['username'] . "<br>";
}
$db->close();
?>