UnitOfWork pattern question : The Official Microsoft ASP.NET Forums

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UnitOfWork pattern question

May 31, 2012 01:13 PM|LINK

Is using UnitOfWork and repositories overkill in an MVC 3 EF4 app since DbContext inherently supports the UnitOfWork concept?

I have a DataContext in my project like this:

public class DataContext : DbContext
{
    #region Constructor

    public DataContext() : base("MyDatabaseName") { }

    #endregion

    #region Properties

    public DbSet<Department> Departments { get; set; }
    public DbSet<Role> Roles { get; set; }
    public DbSet<SampleRequest> SampleRequests { get; set; }
    public DbSet<User> Users { get; set; }

    #endregion

    #region Overrides

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<SampleRequest>()
            .HasRequired(s => s.RequestedBy)
            .WithMany(u => u.SamplesRequested)
            .HasForeignKey(s => s.RequestedById)
            .WillCascadeOnDelete(false);

        modelBuilder.Entity<SampleRequest>()
            .HasRequired(s => s.ApprovedBy)
            .WithMany(u => u.SampleRequestsApproved)
            .HasForeignKey(s => s.ApprovedById)
            .WillCascadeOnDelete(false);
    }

    #endregion
}

From what I gather, I should also have an IUnitOfWork that the DataContext implements.

public interface IUnitOfWork
{
    void Begin();
    void Commit();
    void RollBack();
}

How do I implement Begin and RollBack?

Moved by ignatandrei on May 31, 2012 02:26 PM

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Re: UnitOfWork pattern question

May 31, 2012 01:53 PM|LINK

DbContext already implements unit of work internally -- and all this means is that when you call Save Changes it has a transaction for all of the activity performed against the same instance. So if you want to implement the UoW pattern on top of this, just make sure any repositories you hand out from some unit of work factory all end up referring back to the same instance of the DbContext class.

Brock Allen | http://brockallen.com
DevelopMentor | http://www.develop.com
thinktecture | http://www.thinktecture.com/

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outhowz42

Member

80 Points

121 Posts

Re: UnitOfWork pattern question

May 31, 2012 02:29 PM|LINK

What would be the reason for implementing UOW on top of DbContext if it already internally implements UOW?

Here is the structure I have now, just looking for advice as to whether or not this is following best practices. I am not posting all code for the project, just concentrating on Users and Roles for now. Here is some of the project structure

Folder >> Files:

Controllers >> AccountController, UsersController, RoleController

DAL >> DataContext, DataContextInitializer, IUserRepository, UserRepository, IRoleRepository, RoleRepository, UnitOfWork

Models >> AccountModels, User, Role

ViewModels >> RoleViewModel, UserEditViewModel

//LEAVING OUT MOST ACTION RESULT METHODS FOR BREVITY...
public class UserController : Controller
{
    private UnitOfWork unitOfWork = new UnitOfWork();

    //
    // GET: /User/

    public ActionResult Index()
    {
        return View(unitOfWork.UserRepository.GetUsers());
    }
    
    //
    // GET: /User/Edit/5

    public ActionResult Edit(Guid id)
    {
        User user = unitOfWork.UserRepository.GetUserByID(id);
        if (user == null)
        {
            return HttpNotFound();
        }
        return View(new UserEditViewModel(user, unitOfWork.RoleRepository.GetRoles()));
    }

    //
    // POST: /User/Edit/5

    [HttpPost]
    public ActionResult Edit(UserEditViewModel userEditViewModel)
    {
        if (ModelState.IsValid)
        {
            unitOfWork.UserRepository.UpdateUser(userEditViewModel);
            unitOfWork.Save();
            return RedirectToAction("Index");
        }
        return View(unitOfWork.UserRepository.GetUserByID(userEditViewModel.UserId));
    }

    protected override void Dispose(bool disposing)
    {
        unitOfWork.Dispose();
        base.Dispose(disposing);
    }
}

public interface IUserRepository : IDisposable
{
    IEnumerable<User> GetUsers();
    User GetUserByID(Guid userID);
    void InsertUser(User user);
    void DeleteUser(Guid userID);
    void UpdateUser(User user);
    void Save();
}

public class UserRepository : IUserRepository, IDisposable
{
    #region Member Fields
        
    private DataContext context;

    #endregion

    #region Constructor(s)
        
    public UserRepository(DataContext context)
    {
        this.context = context;
    }

    #endregion

    #region IUserRepository Members
        
    public IEnumerable<User> GetUsers()
    {
        return context.Users.OrderBy(u => u.LastName).OrderBy(u => u.FirstName).ToList();
    }
    public User GetUserByID(Guid userID)
    {
        return context.Users.Find(userID);
    }
    public void InsertUser(User user)
    {
        context.Users.Add(user);
    }
    public void DeleteUser(Guid userID)
    {
        User user = context.Users.Find(userID);
        context.Users.Remove(user);
    }
    public void UpdateUser(User user)
    {
        context.Entry(user).State = EntityState.Modified;
    }
    public void UpdateUser(UserEditViewModel userEditViewModel)
    {
        User user = GetUserByID(userEditViewModel.UserId);

        user.UserName = userEditViewModel.UserName;
        user.Email = userEditViewModel.Email;
        user.FirstName = userEditViewModel.FirstName;
        user.LastName = userEditViewModel.LastName;
        user.PhoneExtension = userEditViewModel.PhoneExtension;
        user.IsApproved = userEditViewModel.IsApproved;

        foreach (RoleViewModel rvm in userEditViewModel.RoleViewModels)
        {
            if (rvm.Checked)
            {
                //add role if it doesn't exist
                var roleToAdd = (from role in context.Roles
                                    where role.RoleId.Equals(rvm.Id)
                                    select role).First();

                if (roleToAdd != null)
                    user.Roles.Add(roleToAdd);
            }
            else
            {
                //remove role
                var roles = from role in user.Roles
                            where role.RoleId.Equals(rvm.Id)
                            select role;

                if (roles.Count() == 1)
                    user.Roles.Remove(roles.ElementAt(0));
            }
        }
        context.Entry(user).State = EntityState.Modified;
    }
    public void Save()
    {
        context.SaveChanges();
    }

    #endregion

    //disposal stuff removed for brevity
}

public class UnitOfWork : IDisposable
{
#region Member Fields
        
private DataContext context = new DataContext();

#endregion

#region Properties

public RoleRepositoroy RoleRepository
{
    get
    {
        if (_roleRepository == null)
            _roleRepository = new RoleRepositoroy(context);

        return _roleRepository;
    }
}private RoleRepositoroy _roleRepository;
public UserRepository UserRepository
{
    get
    {
        if (_userRepository == null)
            _userRepository = new UserRepository(context);

        return _userRepository;
    }
}private UserRepository _userRepository;

#endregion

#region Methods

public void Save()
{
    context.SaveChanges();
}

#endregion

#region IDisposable Members

private bool disposed = false;

protected virtual void Dispose(bool disposing)
{
    if (!this.disposed)
    {
        if (disposing)
        {
            context.Dispose();
        }
    }
    this.disposed = true;
}
public void Dispose()
{
    Dispose(true);
    GC.SuppressFinalize(this);
}

#endregion
}

Now just a few questions.

1. In my UserController I declare a UnitOfWork. I believe I should be injecting this into the controller instead for testability. How can I do that?

2. Is it OK if my repository knows about my UserEditViewModel?

3. Should UnitOfWork be an IUnitOfWork instead that my DataContext implements?

4. Is it pointless to use repositories and IRepositiory? Should I just be using the DbSets in the DataContext class?

Thanks!!

Edited by outhowz42 on May 31, 2012 02:31 PM

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BrockAllen

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Re: UnitOfWork pattern question

May 31, 2012 03:18 PM|LINK

outhowz42

What would be the reason for implementing UOW on top of DbContext if it already internally implements UOW?

To abstract the data layer for testing.

outhowz42

1. In my UserController I declare a UnitOfWork. I believe I should be injecting this into the controller instead for testability. How can I do that?

http://bradwilson.typepad.com/blog/2010/10/service-location-pt5-idependencyresolver.html

outhowz42

2. Is it OK if my repository knows about my UserEditViewModel?

No. ViewModels belong to the UI layer. The dependency should be the other way.

outhowz42

3. Should UnitOfWork be an IUnitOfWork instead that my DataContext implements?

Yes, again for testing. Your UnitOfWork class is concrete and tightly bound to the DbContext (and thus a "real" DB). You don't want the real DB involved while running unit tests. But other than that your UoW code looks spot on (given the brief glance I gave it :).

outhowz42

4. Is it pointless to use repositories and IRepositiory? Should I just be using the DbSets in the DataContext class?

If you can mock them for testing, then you can. But since that tends to be a pain people tend to go with interfaces.

Brock Allen | http://brockallen.com
DevelopMentor | http://www.develop.com
thinktecture | http://www.thinktecture.com/

Marked as answer by outhowz42 on May 31, 2012 07:15 PM

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outhowz42

Member

80 Points

121 Posts

Re: UnitOfWork pattern question

May 31, 2012 03:30 PM|LINK

Thanks for the feedback.

As a follow up to question 2. I agree that the repository shouldn't know about the ViewModel. However, where do I put that mapping logic then? Prior to moving it into the repository it was just in the controllers HttpPost Edit ActionResult. As far as I know, the controllers shouldn't be littered with all of that logic so I need to move it somewhere but where?

Should there be another services layer that essentially maps the updated properties in the view model to the domain model, which then accesses the "naked" UpdateUser method in the repository?

public void UpdateUser(User user)
{
    context.Entry(user).State = EntityState.Modified;
}

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BrockAllen

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Re: UnitOfWork pattern question

May 31, 2012 03:41 PM|LINK

So the repository should be defined in terms of domain entities -- classes defined by the data layer. It's then up to the UI to map. You can do this in a controller's action, or you could do this in the view model itself. Also, I've seen extension methods that do the mapping. There's no hard & fast rule, but you're right when you want to keep things clean.

Brock Allen | http://brockallen.com
DevelopMentor | http://www.develop.com
thinktecture | http://www.thinktecture.com/

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outhowz42

Member

80 Points

121 Posts

Re: UnitOfWork pattern question

May 31, 2012 03:53 PM|LINK

Ok, so if I move the logic around I no longer have any reference to a ViewModel in the UserRepository. I now have a method in the UserEditViewModel to perform the updates. My HttpPost Edit ActionResult in the UserController has also been updated. Does this seem acceptable?

//In UserEditViewModel I have this new method

public User UpdateDomainModelUser(User user, IEnumerable<Role> roles)
{
    user.UserName = this.UserName;
    user.Email = this.Email;
    user.FirstName = this.FirstName;
    user.LastName = this.LastName;
    user.PhoneExtension = this.PhoneExtension;
    user.IsApproved = this.IsApproved;

    foreach (RoleViewModel rvm in this.RoleViewModels)
    {
        if (rvm.Checked)
        {
            //add role if it doesn't exist
            var roleToAdd = (from role in roles
                                where role.RoleId.Equals(rvm.Id)
                                select role).First();

            if (roleToAdd != null)
                user.Roles.Add(roleToAdd);
        }
        else
        {
            //remove role
            var roleToRemove = from role in roles
                        where role.RoleId.Equals(rvm.Id)
                        select role;

            if (roleToRemove.Count() == 1)
                user.Roles.Remove(roleToRemove.ElementAt(0));
        }
    }

    return user;
}

//And here is the updated UserController ActionResult

[HttpPost]
public ActionResult Edit(UserEditViewModel userEditViewModel)
{
    if (ModelState.IsValid)
    {
        User user = unitOfWork.UserRepository.GetUserByID(userEditViewModel.UserId);
        userEditViewModel.UpdateDomainModelUser(user, unitOfWork.RoleRepository.GetRoles());
        unitOfWork.Save();
        return RedirectToAction("Index");
    }
    return View(unitOfWork.UserRepository.GetUserByID(userEditViewModel.UserId));
}