Trying to wrap my brain around generics...

At least, I think that's what I think I want to wrap my head around ;-)

Brief problem statement: How can I write a method signature in a base class that returns a different type depending on the base class? In other words, I want all subclasses to have this method and return something, but what they return might be an int, float, etc. depending on the subclass.

More detailed:
I am writing some classes to talk to a SQL database. I'm desperately trying to avoid "one class per table" because there are lots of tables. There's only four possible data types (int, float, datetime, string), so I thought I'd do this:

• Define a base class called DBType:
  
  • String columnName
  • setValue() that would be overloaded
  • int maxLength (for Strings)
  • toSql() function that would return the appropriate value for a Parameter.Add() binding statement. i.e., it'd return an int, float, DateTime, or String depending on the subclass
  • functions like insert(), update(), and delete(), or perhaps Save() (upsert) and Remove() (delete) - you get the basic idea
• Write four classes that extend this (DBT_Integer, DBT_Float, etc.). They would have constructors that would take care of additional specific defaults (string can only be so long, validation of date ranges, etc.)

Here's the problem, though...how do I write toSql() in the base class? What I'd like it to do is say "I'm going to return a value, but it could be an int, float, DateTime, or String. You won't really care because you'll call it like this: Parameter.Add("id",something.toSql()).

Or perhaps I've gone into some OOP design rabbithole and need to rethink things...

BTW, using an object database (like db4o or something) is not really an option in this case.

I am thinking you want something like this?

Code:

---

    public class GenericClass<T>
    {
        public virtual T ReturnValue()
        {
            return default(T);
        }
    }

    public class IntClass : GenericClass<int>
    {
        public override int ReturnValue()
        {
            return 10;
        }
    }

---

why not just try LINQ to SQL or the Entity Framework? it does all this for you.

Why not just return object and call AddWithValue instead?