newbie here. I am trying to learn OOD/OOP and read on the net that I am not supposed convert SQL tables into classes. But I cannot find an explanation why not to do it or which tables to skip. So I made an web application based on the below diagram. It works perfectly well. But I do not use OO. Would someone please explain simply which table should not be mapped into a class and why not. Thank you for your time.
P.S. Please do not use LINQ or NHibernate, etc as I do not understand them. I just need to understand the OOD.
When designing an application in .NET (and probably most other languages), every table needed by the application becomes its own class, but you can certainly have more classes that are not mapped to table.
With your program’s requirements in hand, you need to design the database layer (i.e. your tables) to persist any data you want saved in a database. Then – for a small project – each table becomes a class automatically and you can start building more classes to manage these “model” or “entity” classes. Classes mapped to tables are often called entities or models. Classes that are not mapped are just called classes.
So, in your example, you have four tables, so you will have at LEAST four model classes. You would then design additional non-model classes (as needed and makes sense) to manage your model classes appropriately through your program.