PDO refuses to switch between multiple Databases!

Answer 1

It appears that your getDB function will only connect once because of this line:

if (!self::$objInstance){

So the first time you execute it, it will connect, but on all subsequent calls the logic is ignored.

I suggest adding another property to your class that stores the current DBType and changing your conditional to:

if (!self::$objInstance || $DBtype != self::$dbtype){

You would have to set $dbtype inside each case of the switch statement.

Answer 2

You have it setup as a singleton. So your next call to Db::getDB returns the original instance. If you want to cache the instances for the duration of the script, change $objInstance to an array, and then instead of doing:

if (!self::$objInstance){

Do

$signature = $DBtype . $DBindex;
if (!isset(self::$objInstances[$signature])) {

Of course you'll need to change the assignment lines and the return line as well, but I think you get the idea...