Question

I have to pull data from at least 3 databases, is there anything wrong with reusing my PDO objects?

$dbh = new PDO('mysql:host=' . $host . ';dbname=' . $db_name, $user, $password);
$sth = $dbh->prepare($query1);

// do something

$dbh = new PDO('mysql:host=' . $host2 . ';dbname=' . $db_name2, $user2, $password2);
$sth = $dbh->prepare($query2);

//do something else

Sorry for the edit but here’s another consideration. With each of these I obviously should check whether or not the connection was successful and throw an exception if it wasn’t:

if (!$dbh) {
    $err=$dbh->errorInfo();
    throw new Exception('Could not connect: ' . $err[2]);
}

I don’t suppose there’s a way to avoid this, unless I create all the connections at the same time and do if (!dbh1|!dbh2) { ... }. Just something else to consider.

Answer 1

When you assign $dbh to a new PDO() you are not technically reusing your pdo object. You are creating a new PDO instance and assigning it to a variable that you have previously used. There is nothing wrong with doing this as long as you understand what is occurring in your program.

EDIT:

I’m editing my answer to address the new question you’ve added to your previous question.

With each of these I obviously should check whether or not the connection was successful and throw an exception if it wasn’t:

You can surround your connection attempt in a try catch which is a typical strategy for dealing with connection errors:

<?php
    try {
        $dbh = new PDO('mysql:host=localhost;dbname=databaseName', $userName, $password);

        foreach($dbh->query('SELECT * from TableName') as $row) {
            print_r($row);
        }

        $dbh = null;
    } catch (PDOException $ex) {
        print "Error!: " . $ex->getMessage() . "<br />";
        die();
    }
?>