ASP.NET service vs repository layers

Question

What is the difference between a service layer and a repository? I have worked through a lot of demo ASP.NET MVC apps and most of them have just repositories. And some have a mixture of both. When do you use just repositories and when do you use services / or both? The same is true for ASP.NET web apps.

Answer 1

Repositories act just as gateways to your data storage (sql database, xml file etc.) while services usually implement some business rules on your data before sending the data to be saved in the database via a repository.

consider this example:

class UserRepository : IUserRepository
{
   public void Create(User userToCreate)
   {
       //update tracking and save to repository
       _userToCreate.DateCreated = DateTime.Now;
       _dataContext.AddNew(userToCreate);
   }
}


class UserService : IUserService 
{
   private IUserRepository _repository;

   public UserService(IUserRepository repository)
   {
        _repository = repository;
   }

   public void Create(User createdByUser, User userToCreate)
   {
       //implement some business rules
       if(!createdByUser.HasRights(UserRights.CanCreateNewUser))
           throw new Exception("This user '"+createdByUser.Name+"' does not have the rights to create a new user");

       //update rules auditing
       _userToCreate.CreatedByUserId = createdByUser.Id;

       //save entity to repository
       _repository.Create(userToCreate);
   }
}

Then in your Controller action you will use the service directly where all your business rules can be applied. That way you can test you controllers, business rules (services) and persistence (repositories) separately/independently using mocks.

    public ActionResult CreateUser(User newUser)
    {
        if(ModelState.IsValid)
        {
           _userService.Create(this.CurrentUser, newUser);
           if(newUser.Id > 0)
               return RedirectToAction("UserCreated");
        }
        return View(newUser);
    }

Answer 2

A repository typically handles data-access only. A service layer will use a repository, and apply any additional business logic. Think of the repository as a re-usable layer than could be used by anything that wants to access your data. Different apps might have different business rules (that would go in the service layer), but could all use the same repository layer implmentation

Answer 3

Just as a compendium to qntmfred answer please have a look at the following resources:

• Service Layer Guidelines
• Service Layer in Web applications