How do you implement a business logic layer when using entity framework as data access layer?

Question

Say i have 3 layers

layer 1: WPF Project (contains: xaml, viewmodels, mvvm framework)

layer 2: business logic layer (contains: plain c# classes)

layer 3: entity framework (contains: repository/data access classes)

when you dont want to expose your DAL(layer 3) to View(layer 1) how do you implement the business logic layer well? im having a hard time putting values back and forth the BLL objects and DAL entities.

can you please help?

Answer 1

Instead of exposing all of your DAL to View Layer, just exchange your domain objects (EF objects) between all layers. The structure may be similar to the following:

1. Presentation Layer-------- ^
2. BLL --------------------------- | Data objects
3. DAL (Repositories etc.)--- |

So, all of your layers will be disconnected; but they will share the same domain objects. In real world, you can implement a similar structure by creating a seperate dll for Entity Framework entities which is shared by all layers. Note that ObjectContext shall be only visible to DAL (by default, entities and object context are generated in the same dll, you need to seperate this into two dlls).