I'm designing a 3-tiered application using ASP.NET MVC 4. I used the following resources as a reference.

• CodeProject: MVC + N-tier + Entity Framework
• Separating data access in ASP.NET MVC

I have the following desingn so far.

Presentation Layer (PL) (main MVC project, where M of MVC was moved to Data Access Layer):

MyProjectName.Main
    Views/
    Controllers/
    ...

Business Logic Layer (BLL):

MyProjectName.BLL
    ViewModels/
    ProjectServices/
    ...

Data Access Layer (DAL):

MyProjectName.DAL
    Models/
    Repositories.EF/
    Repositories.Dapper/
    ...

Now, PL references BLL and BLL references DAL. This way lower layer does not depend on the one above it.

In this design PL invokes a service of the BLL. PL can pass a View Model to BLL and BLL can pass a View Model back to PL.

Also, BLL invokes DAL layer and DAL layer can return a Model back to BLL. BLL can in turn build a View Model and return it to PL.

Up to now this pattern was working for me. However, I've ran into a problem where some of my ViewModels require joins on several entities. In the plain MVC approach, in the controller I used a LINQ query to do joins and then select new MyViewModel(){ ... }. But now, in the DAL I do not have access to where ViewModels are defined (in the BLL).

This means I cannot do joins in DAL and return it to BLL. It seems I have to do separate queries in DAL (instead of joins in one query) and BLL would then use the result of these to build a ViewModel. This is very inconvenient, but I don't think I should be exposing DAL to ViewModels.

Any ideas how I can solve this dilemma? Thanks.