Question

suppose you have an MVC application with the Model represented by an Entity Framework (EF) that “gets” data from a database and the action methods of the Controller that implements all the business logic. The Controller gets data from the database through the EF.

Imagine that now you create a Repository class that is placed between Controller and Model. This way you have:

1) Controller: implements most of the business logic;

2) A Repository class, responsible to implement simple business logic, provide data to every Controller in the application through methods and get data from the EF;

3) Model: EF classes that gets data from the database and provide them to the Repository class.

Is the Repository class the business service layer or there is the need to add a business layer placed between controllers and repository? In this latter situation we have:

1) Controllers: implements just the request elaboration;

2) Business layer: a set of classes responsible to implement most of the business logic and provide data to every Controller in the application through methods;

3) A Repository class: gets data from the EF and expose methods to the Business layer for querying the database;

4) Model: EF classes that “get” data from the database and provide them to the Repository class.

I do not consider the View because it is not relevant. I hope somebody can make clear for me this distinction. Many thanks

Cheers

Francesco

Answer 1

The definitions you have proposed for Model and Controller differ from the traditional usages of the terms in the MVC pattern – or at least, the pattern as defined by Martin Fowler here.

Usually it is the Model that contains most of the business logic, and the Controller is responsible for managing the flow of information between the View and the Model. To quote from Fowler’s article:

The controller’s job is to take the
user’s input and figure out what to do
with it.

Looking at your actual question with regard to where a Repository should be placed, it would be within the Model, but encapsulated away as part of your data access infrastructure (that is almost the very definition of what a Repository is).

So the Model becomes made up of two key parts – Domain objects which have expressive business logic, and service infrastructure that does things like accessing the data access layer. (Another common approach is to have the Model made up of services which don’t really feature a rich domain model, but still this contains all business logic and data access).

One last thought is be careful about over thinking or abstracting this stuff – keep it as simple as possible and only introduce a new layer to your architecture when you are sure it will give value. For example – EF itself can perform the role of your Repository in most scenarios, so using it directly without the repository layer can remove an unnecessary abstraction.