How I check PDO connected to appropriete database - php

Question

I use this code for check connection to the database(MYSQL).If the database name not available then also it show connect successfully.
if(isset($_REQUEST['submit']))
{
echo $name = $_REQUEST['name'];
echo $pwd = $_REQUEST['password'];
$servername = "localhost";
$username = "root";
$password = "";
try
{
$conn = new PDO("mysql:host = $servername;dbname = pdo",$username,$password);
//echo "Connected successfully";
$conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
echo "connect successfully";
}
catch(PDOException $e)
{
echo "Connection failed: " . $e->getMessage();
}
}

Answer 1

TL;DR
Because your code is using try-catch blocks you can be sure that as long as no exceptions are thrown the connection was successfully established. Otherwise check the error code stored inside the exception to resolve the type of error.
More detailed
Your code makes use of exceptions, so if an error occurred while a connection was attempted established an exception would be thrown. As far as I know the PDO object throws exceptions by default while it is constructed and falls back to silent mode when to instance is created. So you are assured you will be warned if anything bad happens during construction.
Update 1
How to check the database name is available or not in to the database using PDO?
As said you can utilize exceptions. But instead of echoing the exception message you can inspect the returned error code using the PDOException method getCode(). Using php version 5.6.8 I will get the code 1049. You can then check using the following:
try {
$pdo = new PDO($dsn, $username, $passowrd, [
PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
PDO::ATTR_EMULATE_PREPARES => false
]);
}catch(PDOException $exception) {
if($exception->getCode() == 1049) {
echo 'Database does not exist!';
}
// Continue error handling...
}
Update 2: Alternative
Using the same PHP version as above you can avoid selecting a database in the DSN. With this you can fetch a list of accessible databases for the used MYSQL user. Using this list you can check the existence of one or more databases at the same time and avoid the overhead of an exception halting execution of your script.
/*
* I assume you are on localhost.
*/
$pdo = new PDO('mysql:host=127.0.0.1', $username, $password, [
PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
PDO::ATTR_EMULATE_PREPARES => false
]);
$databases = $pdo->query('SHOW DATABASES'); // Does not require a prepared statement since it takes no input.
/*
* The following can be done more elegant/efficient.
*/
$exists = false; // Equals TRUE if the database exists.
$check = 'test'; // Enter the database to check for.
foreach($databases->fetchAll(PDO::FETCH_ASSOC) as list($database)) {
if($database == $check) {
$exists = true;
break;
}
}
Bonus
You are setting the error mode after the PDO instance has been constructed. This can also be done with the fourth parameter of PDO's constructer. I think this leads to more readable code.
I would also recommend setting the configuration PDO::ATTR_EMULATE_PREPARES to false. This ensure prepared statements are always used. The documentation can be found here.
$pdo = new PDO($dsn, $username, $password, [
PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
PDO::ATTR_EMULATE_PREPARES => false
]);
Happy coding!