The difference between bad code and good code

A colleague asked for some advice today on a project that he inherited (which I am extending with a separate module incidentally).

The issue was related to the usage of Entity Framework in the code that he had to maintain, and he needed some advice on how to proceed.  The problem was that the service layer was calling the repository multiple times, but each repository method was wrapped in a separate unit of work.
e.g.

public void DeleteEntity(int entityID)
{
    using (var context = EntityContext())
    {
        var entity = context.Postings.SingleOrDefault(p => p.entityID == entityID);
        context.Entities.DeleteObject(entity);
        context.SaveChanges();
    }
}
and
public Entity GetPosting(int entityID)

{
    using (var context = EntityContext())
    {
        return context.Entities.FirstOrDefault(p => p.entityID == entityID);
    }
}

This caused two problems for the developer, who needed to perform a complex action in his service that referenced multiple repository calls.

1. He had no control over the transactional scope for the repository methods
2. Each operation was on a separate EF context, so the service could not load and entity, edit it, and then save the changes (unless the repository was designed for disconnected entities, which it wasn't).

From a maintainability and testability point of view this was also a very poor design, as the repository methods created instances of dependency object (the service method also created instances of the repositories, making the services inherently untestable).


The version of this design that I implemented for my component follows a similar service/repository/entity pattern, but is implemented in a far more testable and robust manner.

The first improvement over the legacy design is in the dependency management
My service accepts a context and all required repositories in the constructor, and my repositories accepts a context, which allows for improved maintainability (all dependencies are described) and testability (all dependencies can be mocked).  This also allows us to use dependency injection/IoC to create our object instances.

The second improvement was in the Unit of Work design.
Rather than have each repository method as a single unit of work, the service methods are the units of work, so any action within the service uses the same context (as it is passed as a dependency to the repositories that the service uses), and each service call acts as a Unit of Work, calling SaveChanges at the end of the service to ensure that the changes act under a single transaction.
There are limitations to this design (your public service methods become an atomic transaction and you should not call other public methods from within another method) but for simplicity and maintainability it is a pretty good solution.

Below is a simple example of the design I am using, preserving maintainability, testability, and predictability.  I'm not saying it is necessarily the best code around, but it solves a number of issues that I often see in other developers code.

public class HydrantService
{
  public HydrantService(HydrantsSqlServer context, EFRepository<Hydrant> hydrantRepository, EFRepository<WorkOrder> workOrderRepository, EFRepository<HydrantStatus> hydrantStatusRepository)
  {
    _context = context;
    _hydrantRepository = hydrantRepository;
    _workOrderRepository = workOrderRepository;
    _hydrantStatusRepository = hydrantStatusRepository;
  }
  public void createFaultRecord(WorkOrder order)
  {
    HydrantStatus status = _hydrantStatusRepository.GetSingle<HydrantStatus>(x => x.StatusCode == "Fault"); //_context.HydrantStatuses.Where(x => x.StatusCode == "Fault").FirstOrDefault();
    order.Hydrant.HydrantStatus = status;
    _workOrderRepository.Add(order);
    _context.SaveChanges();
  }
}

  public class EFRepository<T>
 {
 public EFRepository(IDbContext context)
 {
    _context = context;
  }   public virtual ICollection GetAll()

  {
    IQueryable query = _context.Set();
    return query.ToList();
  }
}