Question

I started learning design patterns a while ago (only covered facade and abstract so far, but am enjoying it). I’m looking to apply the Abstract pattern to a problem I have. The problem is: Supporting various Database systems using one abstract class and a set of methods and properties, which then the underlying concrete classes (inheriting from abstract class) would be implementing.

I have created a DatabaseWrapper abstract class and have create SqlClientData and MSAccessData concrete class that inherit from the DatabaseWrapper.

However, I’m still a bit confused about how the pattern goes as far as implementing these classes on the Client.

Would I do the following?:

DatabaseWrapper sqlClient = new SqlClientData(connectionString);

This is what I saw in an example, but that is not what I’m looking for because I want to encapsulate the concrete classes; I only want the Client to use the abstract class. This is so I can support for more database systems in the future with minimal changes to the Client, and creating a new concrete class for the implementations.

I’m still learning, so there might be a lot of things wrong here. Please tell me how I can encapsulate all the concrete classes, and if there is anything wrong with my approach.

Many Thanks!

PS: I’m very excited to get into software architecture, but still am a beginner, so take it easy on me. 🙂

Answer 1

It could look something like this:

DatabaseWrapper dbClient = DBFactory.getInstance(DbType.SQL, connectionString);

Almost all design patters just introduce another layer of indirection and/or abstraction. In this case DBFactory is an abstraction layer that selects an appropriate implementation based on DbType enum.