我收到此错误代码:为 foreach() 提供的参数无效

问题描述：

我正在学习 PDO 并且感到非常困惑，我在下面有这段代码，对我来说一切正常，但是我收到了这个错误代码，我不知道该怎么做才能修复它，请帮助我:

I am learning PDO and i am getting very confused, I have this piece of code below and all looks right to me however I'm getting this error code and I don't know what I have to do to fix it, please help me:

<?php
$hostname='localhost';
$username='root';
$password='';

try {
    $dbh = new PDO("mysql:host=$hostname;dbname=stickercollections",$username,$password);
    echo 'Connected to Database<br/>';
    
    $sql = "SELECT * FROM stickercollections";
foreach ($dbh->query($sql) as $row)
    {
    echo $row["collection_brand"] ." - ". $row["collection_year"] ."<br/>";
    }
    
    
    $dbh = null;
    }
catch(PDOException $e)
    {
    echo $e->getMessage();
    }
?>

错误代码

Invalid argument supplied for foreach() in /Applications/XAMPP/xamppfiles/htdocs/GOTSWAPMAIN/index.php on line 11

答

尝试增加错误模式:

<?php
$hostname='localhost';
$username='root';
$password='';

try {
    $dbh = new PDO("mysql:host=$hostname;dbname=stickercollections",$username,$password);

    $dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION); // <== add this line
    echo 'Connected to Database<br/>';

    $sql = "SELECT * FROM stickercollections";
foreach ($dbh->query($sql) as $row)
    {
    echo $row["collection_brand"] ." - ". $row["collection_year"] ."<br/>";
    }


    $dbh = null;
    }
catch(PDOException $e)
    {
    echo $e->getMessage();
    }
?>

pdo.error-handling 说，你也可以使用 pdo.errorcode 和 pdostatement.errorcode(或类似)以获取更多信息，但我认为抛出异常是处理错误连接的更好方法，而不是解析主机等

pdo.error-handling says, you can alternatively use pdo.errorcode and pdostatement.errorcode (or like) to get more info, but I think throw exception is better way to handle bad connections, not resolved hosts etc.

我收到此错误代码:为 foreach() 提供的参数无效

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