使用PHP和PDO检查用户名是否存在? [英] Check username exists using PHP and PDO?

问题描述

我有一个db.php文件，其中包含以下内容:

I have a db.php file that has the following in it:

// db.php file
// creates connection to database

// DATABASE CONNECTION FUNCTION
function sql_con(){
    try{
        $dbh = new PDO("mysql:host=".DB_HOST.";dbname=".DB_NAME, DB_USER, DB_PASS,
            array(PDO::MYSQL_ATTR_INIT_COMMAND => "SET NAMES utf8"));

        $dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

    } catch (PDOException $e) {
        // log error to file and display friendly error to user
        ExceptionErrorHandler($e);
        exit;
    }
}

我有一个注册页面，我想检查用户名是否已经存在，所以我事先调用了我的sql_con();函数以连接到数据库，然后执行以下查询

I have a signup page and i want to check if username already exists, so i call my sql_con(); function beforehand to connect to database then do the below query

    // connect to database
    sql_con();

    $stmt = $dbh->prepare("SELECT `user_login` FROM `users` WHERE `user_login` = ? LIMIT 1");
    $stmt->execute(array($username));

    if ( $stmt->rowCount() > 0 ) {
        $error[] = 'Username already taken';
    }

我对PDO还是很陌生，因此我遇到以下错误:

I'm very new to PDO and with the above i get the following errors:

注意:未定义的变量:第64行的C:\ wamp \ www \ signup.php中的dbh

Notice: Undefined variable: dbh in C:\wamp\www\signup.php on line 64

致命错误:在非对象中调用成员函数prepare() C:\ wamp \ www \ signup.php在第64行

Fatal error: Call to a member function prepare() on a non-object in C:\wamp\www\signup.php on line 64

可能有些非常愚蠢的东西，而且我似乎在初学阶段就将自己与PDO混淆了.谁能告诉我我在做什么错?另外，我不确定这是否是正确的方法，因为我是PDO的新手，所以如果有更有效的方法来执行用户名查询检查，请告诉我.

Probably something very silly and I seem to confuse myself with PDO as I'm at the beginner stages. Could anyone tell me what I am doing wrong? Also I am not sure if this is the correct way as I'm new to PDO so if there's a more efficient way to do the username query check then please let me know.

推荐答案

这是因为由于范围的原因，$dbh对象仅限于try catch块和您的sql_con()函数内部.

This is because the $dbh object is limited to inside the try catch block and your sql_con() function due to scope.

正确的解决方案是删除try catch块，并 在sql_con()函数结束时返回$dbh变量 .

The correct solution would be to remove the try catch block, and return the $dbh variable at the end of the sql_con() function.

然后:

try {
    $dbh = sql_con();

    $stmt = $dbh->prepare("SELECT `user_login` FROM `users` WHERE `user_login` = ? LIMIT 1");
    $stmt->execute(array($username));

    if ( $stmt->rowCount() > 0 ) {
        $error[] = 'Username already taken';
    }
}
catch (PDOException $e) {

    //Do stuff with $e

}

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