PHP class design with methods requiring database access
OOP is definitely the way to go. The best advise I can offer is to read the book "Clean Code" by Uncle Bob. The code there is in Java but all principles apply equally to any other language.

I would definitely abstract the DB interface so I can use for any other database, even if you don't plan it in the next future. I have posted small data store architecture code that may help you.

From a look at your code, I am a bit confused by the naming connect and connection and the latter stores $connect in the constructor. Maybe give a more descriptive names (one of the top recommendations in the mentioned book).


Why are you unsetting $connect?
The names such as $LNK_ID are cryptic for reader.
I would reserve a separate class dealing with the database via thin interface (see my post) and let other classes only talk to that class instead of DB directly.