How can an object-oriented programmer get his/her head around database-driven programming?

Question

I have been programming in C# and Java for a little over a year and have a decent grasp of object oriented programming, but my new side project requires a database-driven model.

Answer 1

The products shouldn't even know that the categories exist, much less have a data field containing a category ID!

I disagree here, I would think that instead of supplying a category id you let your orm do it for you. Then in code you would have something like (borrowing from NHib's and Castle's ActiveRecord):

class Category
  [HasMany]
  IList Products {get;set;}

...

class Product
  [BelongsTo]
  Category ParentCategory {get;set;}

Then if you wanted to see what category the product you are in you'd just do something simple like:

Product.ParentCategory

I think you can setup the orm's differently, but either way for the inheritence question, I ask...why do you care? Either go about it with objects and forget about the database or do it a different way. Might seem silly, but unless you really really can't have a bunch of tables, or don't want a single table for some reason, why would you care about the database? For instance, I have the same setup with a few inheriting objects, and I just go about my business. I haven't looked at the actual database yet as it doesn't concern me. The underlying SQL is what is concerning me, and the correct data coming back.

If you have to care about the database then you're going to need to either modify your objects or come up with a custom way of doing things.