OO Design vs Database Design

Question

Suppose I am developing an application for a product distributor in C#.

The distributor does the following 3 types of transactions:

(1) Indent

(2) Sell

(3) Stock

I am designing my classes as follows:

public abstract class Transaction
{
}

public class Indent : Transaction
{
}

public class Sell : Transaction
{
}    

public class Stock : Transaction
{
}

Now if I want to save these three types of information in three separate tables then how should I design my DA layer?

Should I build separate DA classes like

(1) IndentDA
(2) SellDA
(3) StockDA

or a single class TransactionDA and perform CRUD operations by checking their types by using as/is operators?

Or what else can I do? Any suggestions?

Answer 1

Firstly, if you created a single class TransactionDA and checked types inside the class to perform CRUD operations, you would be violating the Open/Closed Principle, so I would definitely not go down that path.

As for suggestions on how to accomplish building out your DAL, I would suggest following some blog posts on people much smarter than I on what they think about this topic.

Repository is the new Singleton

Repository is Dead: Long Live Repository

Night of the Living Repositories

The conversation continues, I believe, but that should get you started.