php mysql封装类

<?php
class Database {
    private $host = "localhost";
    private $username = "root";
    private $password = "";
    private $dbname = "mydatabase";
    private $conn;

    public function __construct() {
        try {
            $this->conn = new PDO("mysql:host=$this->host;dbname=$this->dbname", $this->username, $this->password);
            $this->conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
        } catch (PDOException $e) {
            echo "Connection failed: " . $e->getMessage();
        }
    }

    public function query($sql) {
        try {
            $stmt = $this->conn->query($sql);
            return $stmt->fetchAll(PDO::FETCH_ASSOC);
        } catch (PDOException $e) {
            echo "Query failed: " . $e->getMessage();
        }
    }

    public function insert($table, $data) {
        $keys = implode(', ', array_keys($data));
        $values = ':' . implode(', :', array_keys($data));
        $sql = "INSERT INTO $table ($keys) VALUES ($values)";
        try {
            $stmt = $this->conn->prepare($sql);
            $stmt->execute($data);
            return true;
        } catch (PDOException $e) {
            echo "Insert failed: " . $e->getMessage();
        }
    }

    public function update($table, $data, $where) {
        $set = '';
        foreach ($data as $key => $value) {
            $set .= "$key = :$key,";
        }
        $set = rtrim($set, ',');
        $sql = "UPDATE $table SET $set WHERE $where";
        try {
            $stmt = $this->conn->prepare($sql);
            $stmt->execute($data);
            return true;
        } catch (PDOException $e) {
            echo "Update failed: " . $e->getMessage();
        }
    }

    public function delete($table, $where) {
        $sql = "DELETE FROM $table WHERE $where";
        try {
            $stmt = $this->conn->prepare($sql);
            $stmt->execute();
            return true;
        } catch (PDOException $e) {
            echo "Delete failed: " . $e->getMessage();
        }
    }
}
?>