How and where to map EF POCOs to Business Objects - linq

Question

I have the projects
Domain.Model (contains code first POCOs)
Data.Context (contains the context & migrations only)
Data.Access (contains IGenericRepository & GenericRepository)
Service (contains BL service classes and UnitsOfWork)
Presentation.Admin (an Asp.Net Webforms web application)
I am using my POCOs as business objects across all the layers. I know there is some debate about this but this also fairly accepted.
So I have the Presentation calling Service > Getting a POCO via the Repository > Returning to Presentation and displaying, for example a HTML table and saving edits back to the DB - great.
Now I have a more complex page which I think requires a business object. This is a made-up by analogous example.
POCO
public class Book
{
BookId
string ExternalReference
}
public class Movie
{
int MovieId
string ExternalReference
}
Suggested Business Object
public MovieAdaptation
{
Book book;
Movie movie;
}
So ExternalReference is external and can not be a common foreign key in my database so therefore i cannot just do Book.Movie using a navigation property. I need to do a LINQ join (probably).
So my questions are:
1) Where should I define this business object. Currently it is just in the Service layer as only things that reference the service layer will use it.
2) Where should I construct this business object? Should it be in repositories which sit in Data.Access or further up?
3) How do I construct it using LINQ. Here is my best shot so far, but it seems pretty inefficient, especially if I am returning a list of these.
namespace MyProject.Services
{
public class AdaptationsService
{
AdaptationUnitOfWork _unitOfWork;
public AdaptationService
{
unitOfWork = new AdaptationUnitOfWork();
}
public Adaption GetAdaptations(string externalReference)
{
//Can anyone improve this maybe using LINQ join (as maybe it won't be getting books/movies by SingleOrDefault but by where
Book book= _unitOfWork.BookRepository.Get.SingleOrDefault(b=>b.ExternalReference==externalReference);
Movie movie= _unitOfWork.MovieRepository.Get.SingleOrDefault(m=>m.ExternalReference==externalReference);
Adaptation adaptation = new Adaptation();
adaptation.Book=book;
adaptation.Movie=movie;
}
}
}

Answer 1

1) Where should I define this business object. Currently it is just in the Service layer as only things that reference the service layer will use it.
I would probably keep it in the Service Layer. It's not relevant to your DAL as it's a combination of your POCO's, not the POCO's themselves. Have the Service layer construct/destruct it (see below).
2) Where should I construct this business object? Should it be in repositories which sit in Data.Access or further up?
Construct and destruct it in the Service Layer. The DAL should only send and receive your data access objects (your POCOs). Constructing and destructing business objects is not part of it's job description. For all intents and purposes whenever you use the term business object it should be above the DAL.
3) How do I construct it using LINQ. Here is my best shot so far, but it seems pretty inefficient, especially if I am returning a list of these.
I don't have a better answer than the example you gave. It sounds like you have to perform 2 queries then construct it yourself as you're doing.