Question

I have been looking around for an answer to my question but couldn’t find one, mostly because I don’t really know how to phrase it!

I am playing around with EF code first and trying to implement some sort of repository pattern whilst using dependency injection (thanks to Unity). I am also trying to keep to SOLID (well, the SRP part at least) in that I have IStaffRepository and IDepartmentRepository interfaces which in turn implement IRepository<TEntity> which provides basic CRUD methods.

My question is, how can I keep to the SRP when I need to update a staff members’ department?

I have read that it is bad practice to use a single DbContext instance for all repositories due to possible memory leaks and so I cannot simply call the IDepartmentRepository to get the new department as this would use a separate instance of my DbContext.

The obvious solution to me is to include something like…

Department GetDepartment(int id);

Within IStaffRepository – but would this not break the SRP?

The code I have in my Controller is…

private IStaffRepository repository;
private IDepartmentRepository departmentRepository;

public StaffController(IStaffRepository repository, IDepartmentRepository departmentRepository)
{
   this.repository = repository;
   this.departmentRepository = departmentRepository;
}

public ActionResult Edit(int id)
{
   return View(new StaffViewModel(repository.GetItem(id)));
}

[HttpPost]
public ActionResult Edit(int id, StaffViewModel model)
{
   if (!ModelState.IsValid)
      return View(model);

   var item = repository.GetItem(id);

   // throws error due to different context
   item.Department = departmentRepository.GetItem(int.Parse(model.SelectedDepartment));

   UpdateModel(item, "Item");

   repository.Save();

   return RedirectToAction("Member", new {id});
}

And the StaffMember model contains…

public class StaffMember
{
   public virtual Department Department { get; set; }
}

And the StaffViewModel looks like this…

public class StaffViewModel : ViewModelBase<StaffMember>
{
   public SelectList DepartmentList {get;set;}
   public string SelectedDepartment {get;set;}

   public StaffViewModel()
   {
      var departmentRepository = new DepartmentRepository();
      DepartmentList = new SelectList(departmentRepository.GetCollection(), "ID", "Title", SelectedDepartment);   
   }

   public StaffViewModel(StaffMember item) : this()
   {
      Item = item;
      SelectedDepartment = Item.Department.ID.ToString();
   }

   public StaffViewModel(List<StaffMember> collection) : this()
   {
      Collection = collection;
   }
}  

In the database there is a int Department_ID field which hooks up to the Department table.

I have a drop down in my view which looks like…

@Html.DropDownListFor(m => m.SelectedDepartment, Model.DepartmentList, "--Please Select--")

Apologies for the length of this question!

Answer 1

If all of your models are based on entities in the same database, there is not reason not to use a single context instance to manage them within the same controller. I would go with the simple solution and use a single context instance.