Question

I am trying to create 3-tier winform application. Since this is my first attempt of 3-tier design, I got stuck and have few questions.

The application will support attaching multiple sqlite db files.

So I created class like this

public class Database
{
    public string Name { get; set; }
    public string FilePath { get; set; }
    public bool isAttached { get; private set; }
}

Now I want to have collection of those objects.

Should I create another class like DatabaseList below or is enough to just create a List

public class DatabaseList : List<Database>
{
...

vs

List<Database> myDatabases;

What should be created in Form1.cs?

For example I assume the collection above should be created in BusinessLayer and not in Form1.cs and only BusinessLayer class is created in Form1.cs. Is this correct?

Where to put Attach Method?

The method would be like this:

    public void AttachDB(Database db)
    {
        MySqliteHelper.Attach(db.Name, db.FilePath);
        this.Add(db);
    }

Do I put the method in DatabaseList class (if this is the way to create collection) or should it be in BusinessLayer?

How to make the Attach method to support additional relational databases like MS SQL Compact Edition which also resides in a single file

I was thinknig of creating another general database helper class with same methods as MySqliteHelper and the AttachDB method would call that instead. Something like

MyDBHelper.Attach(db.Name, db.FilePath);

Or is this where Dependency Injections like Ninject can be helpful? I never used that before and all I am recalling from Ninject is a samurai having different weapons so it seems to me to be kinda similar to my problem having different specific database classes.

Answer 1

What you lack is thinking in terms of objects and their responsibility.

What object is responsible for creating instances of your database descriptions? Should it be Form1?

The OOP tells you that if you have such doubts you can follow the Pure Fabrication principle and just create another class to be responsible for this. This is just as simple.

So you can create a class, let call it DatabaseManager, put your list of databases there plus the Attach method. You probably also want this manager to be an ambient class (the same instance shared among other classes) so you can build a Singleton out of it (but this is not necessary).

DI containers could probably help you to organize services and manage their lifetime but I recommend you start with a good book on this before you misuse the idea. Mark Seemann’s “Dependency Injection in .NET” is fine.