Question

I have a section of code that depending on the URL requested, will include one of fourteen other files. Some of these fourteen files require a connection to one of three different databases, and additional files can be added at anytime.

I don’t want to open PDO connections by default to all three database as its a waste of resources and will slow the execution time down. So my thought is to wrap all SQL queries within a function. The first time that a query is executed on a non-open PDO connection, the try {} error handler can catch it, find out what the problem was (in this case connection doesnt exist), then open the connection and re-execute the query. That way, the database is only being connected to as and when needed – as long as the connection string (host, database, username, password) are all defined in advance, I can’t see any problem in it working.

However, I need to push on with this, and don’t have access to the dev box for about 7 days, so can anyone see any problem with that scenario? Also, can anyone give me the error message that handler->errorInfo() will return if the connection isn’t opened?

Answer 1

This is the right idea, but not the best implementation of it.

Wrapping the SQL operations is good. But why don’t you do it this way:

class Wrapper {
    private static $db;

    public static function someQuery() {
        $db = self::getDatabase();
        // now go on to execute the query
    }

    private static function getDatabase() {
        if (self::$db === null) {
            self::$db = // connect here
        }
        return self::$db;
    }
}

This has a lot of advantages:

• Allows you to logically group SQL operations into one (or several!) classes
• Does not connect to database if not needed
• Does not depend on (brittle) error checks to function correctly

In your specific case, you should probably go with 3 separate Wrapper classes. Putting everything into one class is doable (three different $db variables) but probably more confusing than it’s worth.