try catch in PHP5 PDO - pdo

Question

This is my third day on PHP. I have the following code for selecting data-
$conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
$conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
try
{
$sql = "SELECT LoginName FROM users WHERE LoginName = :LoginName";
$statement = $db->prepare($sql); //intentionally used $db here
$statement->bindParam(':LoginName', $LoginName, PDO::PARAM_STR, 50);
$statement->execute();
$count= $statement->rowCount();
}
catch(PDOException $e)
{
header('Content-Type: application/json');
echo json_encode(array('result'=>'Error','data'=> $e->getMessage()));
}
I intentionally used $db instead of $conn. So there supposed to be an exception. But in my ajax call, $e->getMessage() has not been sent from catch block.
Any help?

Answer 1

Here is how it have to be done
First, set this handler ho handle ALL errors that may occur in your script, be it PDO or anything else.
set_error_handler("myErrorHandler");
function myErrorHandler($errno, $errstr, $errfile, $errline)
{
error_log("$errstr in $errfile:$errline");
header('HTTP/1.1 500 Internal Server Error', TRUE, 500);
header('Content-Type: application/json');
echo json_encode(array('result'=>'Error', 'data'=>'Server error'));
exit;
}
then make your PDO code this way
$conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
$conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$sql = "SELECT 1 FROM users WHERE LoginName = ?";
$statement = $db->prepare($sql); //intentionally used $db here
$statement->execute([$LoginName]);
$found = $statement->fetchColumn();
In essence, you should follow these rules:
never use try catch operator to report an error
never reveal a real error to an outsider. Just a generic message