Check username exists using PHP and PDO? - php

Question

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;
}
}
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';
}
I'm very new to PDO and with the above i get the following errors:
Notice: Undefined variable: dbh in C:\wamp\www\signup.php on line 64
Fatal error: Call to a member function prepare() on a non-object in
C:\wamp\www\signup.php on line 64
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.

Answer 1

This is because the $dbh object is limited to inside the try catch block and your sql_con() function due to scope.
The correct solution would be to remove the try catch block, and return the $dbh variable at the end of the sql_con() function.
Then:
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
}

Answer 2

The $dbh variable is destroyed once the function is done executing.
You could try returning the handle:
function sql_con() {
// your connection code
return $dbh;
}
Then in your signup page:
$dbh = sql_con();
Depending on your needs, a better alternative would be to employ a DI container.

Answer 3

You are defining pdo in function an ist not visible out it.
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);
return $dbh; //this
} catch (PDOException $e) {
// log error to file and display friendly error to user
ExceptionErrorHandler($e);
exit;
}
}
$dbh = sql_con();
It will be better if you create a class for pdo abstraction.
$dbh = DB::getInstance();