具有实体框架6的实用程序DAL层

Question

I'm wondering about the utility of making a dal layer with EF. Why not calling EF directly in business layer, considering EF DBContext is a unitOfWork and List DBSet are repositories ? So why adding an extra DAL layer, wich is finally a facade.. The only advantage i see, is in case of we have to change the data access implementation, like replace EF by Hibernate or other. But honestly, i've never seen that happen.

Answer 1

Actually with a data mapper the necessity of developing a DAL is plain useless because it would contain 0 lines of code.

Everything on top of a data mapper isn't a data access layer but actual domain, because a data mapper implementation like an OR/M translates your objects into the underlying relational data and viceversa, and you work on top of them is to develop your domain and miss the pain of object-relational impedance.

The point of introducing the repository pattern on top of a data mapper is because you want to both be able to switch the underlying data store even to a non-relational one in the long run (also, switch from NoSQL to SQL, who knows!), and there's another definitive reason to introduce the repository layer in your software: because you want to be able to mock the data store with fakes in order to unit test your domain .

Finally, even when Entity Framework implements unit of work and other patterns, sometimes their implementation may not suit your own domain requirements and you need to wrap them to provide more concretion to your domain.