Question

I’m developing an application using asp.net mvc, NHibernate and DDD. I have a service layer that are used by controllers of my application. Everything are using Unity to inject dependencies (ISessionFactory in repositories, repositories in services and services in controllers) and works fine.

But, it’s very common I need a method in service to get only object in my repository, like this (in service class):

public class ProductService {

   private readonly IUnitOfWork _uow;
   private readonly IProductRepository _productRepository;

   public ProductService(IUnitOfWork unitOfWork, IProductRepository productRepository) {
      this._uow = unitOfWork;
      this._productRepository = productRepository;
   }

   /* this method should be exists in DDD ??? It's very common */
   public Domain.Product Get(long key) {
      return _productRepository.Get(key);
   }

   /* other common method... is correct by DDD ? */
   public bool Delete(long key) {
      usign (var tx = _uow.BeginTransaction()) {
         try 
         {
           _productRepository.Delete(key);
           tx.Commit();
           return true;
         } catch {
           tx.RollBack();
           return false;
         }        
      }
   }

   /* ... others methods ... */

}

This code is correct by DDD ? For each Service class I have a Repository, and for each service class need I do a method “Get” for an entity ?

Thanks guys

Cheers

Answer 1

That looks correct from my perspective. I really didn’t like repeating service and repository method names over and over in my asp.net MVC project, so I went for a generic repository approach/pattern. This means that I really only need one or two Get() methods in my repository to retrieve my objects. This is possible for me because I am using Entity Framework and I just have my repository’s get() method return a IQueryable. Then I can just do the following:

Product product = from p in _productRepository.Get() where p.Id == Id select p; 

You can probably replicate this in NHibernate with linq -> NHibernate.

---

Edit: This works for DDD because this still allows me to interchange my DAL/repositories as long as the data library I am using (Nhibernate, EF, etc..) supports IQueryable.

I am not sure how to do a generic repository without IQueryable, but you might be able to use delegates/lambda functions to incorporate it.

---

Edit2: And just in case I didn’t answer your question correctly, if you are asking if you are supposed to call your repository’s Get() method from the service then yes, that is the correct DDD design as well. The reason is that the service layer is supposed to handle all your business logic, so it decides exactly how and what data to retrieve (for example, do you want it in alphabetical order, unordered, etc…). It also means that it can perform validation after loading if needed or validation before deleting and/or saving.

This means that the service layer doesn’t care exactly how that data is stored and retrieved, it only decides what data is stored and retrieved. It then calls on the repository to handle the request correctly and retrieve/store the data in the way the service layer tells it to. Thus you have correct separation of concerns.