Question

我觉得我在PHP中缺少一些关于OOP的东西。我已经阅读了许多关于连接到mysql的教程但是仍然遇到错误，告诉我我的数据库句柄不存在，即使它确实连接了。我有以下代码，一切都正确连接，但是当我尝试关闭连接时（我知道PHP在脚本完成时关闭了连接，但这对我来说也是一个学习练习）与$ connection-＆gt;关（）;我注意到$ database_handle未定义，因此mysqli_close（$ database_handle）引用了一个NULL变量并返回致命错误。

为什么$ connection-＆gt; connect（）; work和$ connection-＆gt; close（）;返回致命错误？

课程：

<?php

class database_connection  {
    var $hostname = 'localhost';
    var $username = 'root';
    var $password = '';
    var $database = 'assistant';
    var $database_handle;

    function connect() 
    {
        $database_handle = mysqli_connect($this->hostname, $this->username, $this->password, $this->database);

        if (!$database_handle) 
        {
            die('Could not connect to database!');
        } 
        else 
        {
            $this->database_handle = $database_handle;
            echo 'Connection established!';
        }
        return $this->database_handle;
    }

    function close() 
    {
        mysqli_close($database_handle);
        echo 'Connection closed!';
    }

}

?>

引用page.php：

<?php

include 'includes/database_classes.php';

$connection = new database_connection();
$connection->connect();
$query = 'SELECT * FROM  `users`';
$result = mysqli_query($connection->database_handle, $query);

if($numrows = mysqli_num_rows($result)) 
{
    echo "<br>";
    echo $numrows;
    echo "<br>";

    while ($row = mysqli_fetch_assoc($result)) 
    {
        $database_username = $row['user_name'];
        $database_password = $row['user_password'];
        echo $database_username;
        echo $database_password;
    }
}

$connection->close();   

?>

Answer 1

我是否可以建议您采用这种方法，以便每个人在脚本上一次只有一个连接

这也解决了你的错误

function close() 
{
    mysqli_close($database_handle); // $database_handle does not exist
    echo 'Connection closed!';
}

到

function close() 
{
    mysqli_close($this->database_handle);
    echo 'Connection closed!';
}

这确保即使您在脚本中多次调用database_connect()方法，它也只会创建一个连接

<?php

class database_connection  {
    private $hostname = 'localhost';
    private $username = 'root';
    private $password = '';
    private $database = 'assistant';
    private $database_handle = NULL;

    function connect() 
    {
        if ( ! isset($this->database_handle) ) {
            // only create a connection if one does not already exist
            $this->database_handle = mysqli_connect($this->hostname,
                                                    $this->username, 
                                                    $this->password, 
                                                    $this->database
                                                   );

            if (!$this->database_handle) {
                die('Could not connect to database!');
            } 
        }    

        return $this->database_handle;
    }

    function close() 
    {
        mysqli_close($this->database_handle);
        echo 'Connection closed!';
    }

}

?>

Answer 2

你可以试试这个。

function close() 
{
    mysqli_close($this->database_handle);
    echo 'Connection closed!';
}

Answer 3

我认为你有一些范围问题，而且你并没有在任何地方使用正确的参数。请尝试下面的内容，如果有帮助请告诉我。

<?php

class database_connection  {
    var $hostname = 'localhost';
    var $username = 'root';
    var $password = '';
    var $database = 'assistant';
    var $database_handle;

    function connect() 
    {
        $this->database_handle = mysqli_connect($this->hostname, $this->username, $this->password, $this->database);

        if (!$this->database_handle) 
        {
            die('Could not connect to database!');
        } 
        else 
        {
            echo 'Connection established!';
            return $this->database_handle;
        }
    }

    function close($database_handle) 
    {
        mysqli_close($database_handle);
        echo 'Connection closed!';
    }
}
?>


<?php

include 'includes/database_classes.php';

$connection = new database_connection();
$connection->connect();
$query = 'SELECT * FROM  `users`';
$result = mysqli_query($connection->database_handle, $query);

if($numrows = mysqli_num_rows($result)) 
{
    echo "<br>";
    echo $numrows;
    echo "<br>";

    while ($row = mysqli_fetch_assoc($result)) 
    {
        $database_username = $row['user_name'];
        $database_password = $row['user_password'];
        echo $database_username;
        echo $database_password;
    }
}

$connection->close($connection);   

?>

数据库句柄和空的连续冲突

3 个答案: