How to implement class diagram with database

Question

I am at beginner stage of OOP. Got an academic project, need to make a UML Class Diagram of C# Code.

I am developing a project which will use database, I am confused about 1 thing. In UML we use inheritance like department and student, we create 2 classes and put department ID in student class.

Coming to my confusion, I will make some classes like department, student and teacher, and also a database with same tables. How can I use classes, because I know that on user request I can process data on database (on runtime), Like adding teacher or student to department, getting all students, etc. I am supposed to get all data from database when program loads? and save data in variables and put it in database when required? Simplifying my confusion, How to use classes when we use database to get data dynamically?

Answer 1

What you are talking about is a transition, which is not inheritance. At least not really. Once you have developed a class model you will think about persistence. The persistence can be designed in many ways (in most cases you will derive just one persistence scheme, though). Now what you do is to "copy" your classes from your design model to a new package for the persistence. Thereby <<trace>> from the persistence back to the design class. Now you almost independently optimize your persistence towards your desired schema. You will introduce primary and foreign keys, redundancy and things like that. Anyhow, your persistence model only remembers where it came from (via the <<trace>>) but it now has a living on his own.

Note that some UML tools offer automated transition from design models to various derivates.