PDO:在非对象上调用成员函数fetch()吗? [英] PDO: Call to a member function fetch() on a non-object?

问题描述

我只是在尝试PDO，但出现此错误，致命错误:在非对象上调用成员函数fetch()，但在$ this-> db对象上已经不是吗?

I am just trying out PDO and I get this error, Fatal error: Call to a member function fetch() on a non-object, but isn't it already on the $this->db object?

class shoutbox {

    private $db;

    function __construct($dbname, $username, $password, $host = "localhost" ) 
    { # db conections
        try {
            $this->db = new PDO("mysql:host=".$hostname.";dbname=".$dbname, $username, $password);
        }
        catch(PDOException $e)
        {
            echo $e->getMessage();
        }
    }

    function getShouts()
    {
        $sql_shouts = $this->db->query('SELECT shoutid, message, pmuserid, ipadress, time FROM shouts WHERE pmuserid == 0');

        return $sql_shouts->fetch(PDO::FETCH_OBJ);

    }

}

推荐答案

仔细查看

Look carefully at the documentation for PDO::query, particularly the "Return Values" section:

PDO :: query()返回一个PDOStatement 对象，如果失败则为FALSE.

PDO::query() returns a PDOStatement object, or FALSE on failure.

重要的一点是失败时为FALSE". FALSE不是对象，因此调用-> fetch()是个坏消息.

The important bit is "FALSE on failure". FALSE is not an object, so calling ->fetch() is bad news.

该错误可能是由于您使用了"=="比较运算符.在SQL中，它只是"=".

The error is probably due to your use of "==" comparison operator. In SQL, it's just "=".

您应该测试$sql_shouts是否为false，然后对错误进行一些巧妙的处理(如果有的话):

You should test that the $sql_shouts is not false, and then do something smart with the error, if there was one:

<?PHP
$sql_shouts = $this->db->query('...');
if ($sql_shouts === false){
    $errorInfo = $this->db->errorInfo();
    //log the error or take some other smart action
}
return $sql_shouts->fetch(PDO::FETCH_OBJ);

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