Basic ASP.NET MVC controller / data layer interaction architecture example.

GadgetController.cs

class GadgetController : Controller {
	// Each MVC controller has a complementing '*ControllerContext' class.
	private readonly IGadgetControllerContext _context;

	GadgetController()
		: this(new GadgetControllerContext()) {	}

	// Unit testing ctor. Allows passing in mock repositories.
	GadgetController(IGadgetControllerContext context) {
		_context = context;
	}

	ActionResult Index() {
		ViewData["gadgets"] = _context.GadgetRepo.GetAll();
		return View();
	}
}

GadgetControllerContext.cs

// Controller Context class for the Gadget controller.
// Provides access to the data repositories needed by the controller.
// Inherits from the base MyAppControllerContext which provides
// the underlying data context / session / connection stuff.
class GadgetControllerContext : MyAppControllerContext, IGadgetControllerContext {
	private readonly IGadgetRepository _gadgetRepo;

	GadgetControllerContext() {
		_gadgetRepo = new GadgetRepository(base.DbSession);
	}

	IGadgetRepository GadgetRepo { get { return _gadgetRepo; } }
}

GadgetRepository.cs

// Data access repository for Gadgets.
// Follows the repository pattern, for better or worse.
class GadgetRepository : IGadgetRepository {
	// TODO: Replace IDbSession with your DataContext or whatever.
	private readonly IDbSession _session;
	GadgetRepository(IDbSession session) {
		_session = session;
	}

	IEnumerable<Gadget> GetAll() {}
}

IGadgetControllerContext.cs

interface IGadgetControllerContext {
	IGadgetRepository GadgetRepo { get; }
}

IGadgetRepository.cs

interface IGadgetRepository {
	IEnumerable<Gadget> GetAll;
}

MyAppControllerContext.cs

// Base class for all *ControllerContext classes.
// Handles opening/closing the underlying data connections/sessions/etc.
class MyAppControllerContext {
    // TODO: Replace IDbSession with your DataContext or whatever.
    IDbSession DbSession { get { return GetSessionForHttpContext(HttpContext.Current); } } 
	
    // TODO: This is also a great place for things like AppSettings, etc.

    /// <summary>
    /// Gets a per-request database unit of work session
    /// </summary>
    /// <author>Joshua Poehls</author>
    public static IDbSession GetSessionForHttpContext(HttpContext ctx)
    {
        return GetSessionForHttpContext(new HttpContextWrapper(ctx));
    }

    private const string DbContextHttpContextItemKey = "MyAppControllerContext.DbSession";

    /// <summary>
    /// Gets a per-request database unit of work session
    /// </summary>
    /// <author>Joshua Poehls</author>
    public static IDbSession GetSessionForHttpContext(HttpContextBase ctx)
    {
        Debug.Assert(ctx != null);

        if (!ctx.Items.Contains(DbContextHttpContextItemKey))
        {
            var dbCtx = new MyAppDbContext();
            ctx.Items.Add(DbContextHttpContextItemKey, dbCtx);

            if (DbSessionInit != null)
            {
                DbSessionInit(dbCtx, new DbSessionInitEventArgs(dbCtx));
            }
        }

        return (MyAppDbContext)ctx.Items[DbContextHttpContextItemKey];
    }

    // TODO: Call DisposeSessionForHttpContext() on Application.EndRequest!
    //       The MyAppControllerContextModule HttpModule does this for you if you wire it up.

    /// <summary>
    /// Disposes any DB context that was created for the
    /// given <see cref="HttpContext"/>.
    /// </summary>
    /// <author>Joshua Poehls</author>
    public static void DisposeSessionForHttpContext(HttpContext ctx)
    {
        Debug.Assert(ctx != null);

        if (ctx.Items.Contains(DbContextHttpContextItemKey))
        {
            var db = (MyAppDbContext)ctx.Items[DbContextHttpContextItemKey];
            if (db != null)
            {
                db.Dispose();
            }
            ctx.Items.Remove(DbContextHttpContextItemKey);
        }
    }
}

MyAppControllerContextModule.cs

/// <summary>
/// Handles disposing the <see cref="MyAppControllerContext"/> object's session when the request ends.
/// </summary>
/// <author>Joshua Poehls</author>
public class MyAppControllerContextModule : IHttpModule
{
    public void Init(HttpApplication context)
    {
        context.EndRequest += Application_EndRequest;
    }

    private static void Application_EndRequest(object sender, EventArgs e)
    {
        var app = (HttpApplication)sender;
        MyAppControllerContext.DisposeSessionForHttpContext(app.Context);
    }

    public void Dispose() { }
}