3-tier MVC application using Unit of Work and Repository pattern

Question

I have a design problem while starting my MVC project. The example that i was following is on the following link: Implementing the Repository and Unit of Work Patterns

1: http://www.asp.net/mvc/tutorials/getting-started-with-ef-5-using-mvc-4/implementing-the-repository-and-unit-of-work-patterns-in-an-asp-net-mvc-application .

In there the unit of work and generic repository are in the data layer project. In my project they are also there, but from what i see they are making an instance from the unit of work class directly into the controller.

Since i made the BAL project i am interested what i will have to change to the current design and what should the BAL project contain (some small code will help a lot).

Here is a screenshot of my current project.

Answer 1

The BAL should contain the Business Logic.

The Controller will use the BAL's API and high-level functions in a bridge pattern and orchestrate data exchanges with the DAL underneath, loading and persisting data, like this:

MyEntity e;
Repository<MyEntity> r;

r = DAL.GetRepository<MyEntity>;
e = r.Retrieve(x => x.Age > 20);
v = BAL.GetValidator<MyEntity>();

e.Broken = !v.Validate(e).HasErrors;
e.LastChecked = DateTime.Now;
DAL.GetRepository("MyEntity").Update(e);

This is not working code, it is just to give the idea of a thin controller. If this repeats too often (like 3 times or more) it's time to consider promoting the code into the BAL, because it might be a commonly accepted procedure of the business.

You can add Unit of Work patterns and using () {} clauses as needed. The problem will always be: what is business logic and was is application logic? What goes into the controller and what into the library?

Generally, try to keep the controllers thin and keep the BAL free of persistence logic and application logic.

Principles like DRY (Don't Repeat Yourself) and KISS (Keep It Simple, Stupid) will guide you along the way. The rest is analysis (practices for requirement gathering) and years of experience in this field. Both can't be taught but require that you keep practicing.