Ninject DI / ASP.Net MVC - How do I add a business layer?

Question

I am writing a silly program to try to fully understand all the various concepts involved in design patterns in a practical way. For example, I fully understand DI / IOC, (I think), but I don't fully understand how to apply it in a practical ASP.Net MVC 4/5 environment.

I am writing a store program with invoices and products as my only 2 tables. So far I have been successful at fully applying DI/IOC and have finished up with the following structure:

Store.Models <== Entity Framework classes. (Data access layer).
Store.Interfaces <== Interfaces.
Store.Repositories <== Contains the code that actually goes and gets or sets the data.
Store.Web <== My MVC application.

All the dependencies are setup and working fine. Now here is my question and problem.

I want to add a business layer as follows:

Store.Business

For the purposes of the exercise I have decided to simply calculate the number of years since a given date. Of course, under normal circumstances I would store this in the database as a calculated field and retrieve it. But I am doing it for the academic exercise because at some point, I will come across a situation where I will have to actually do some complex calculations on a dataset. I am of the opinion that this should not really be stored with the model, repository, or done in the controller. That there should be a separate "business" layer. Now here is my problem:

Entity framework defined a class called Invoice based on my model. Its a fine class, it worked until now.

I defined an interface, and repository, setup Ninject, got it all working with MVC. Everything is perfect. Couldn't be happier.

I then added a date field to the invoice table. Updated my model in EF, updated the other stuff I needed to update and everything went well.

Next I added a Store.Business class project. I setup a new Invoice class which inherited the Invoice class from the model and added a new property, constructor and method.

namespace Store.Business
{
    //NOTE: Because of limitations in EF you cant declare a subclass of the same name.

    public class InvoiceBL : Store.Models.Invoice
    {
        [NotMapped]
        public int Age { get; set; }

        public InvoiceBL()
        {
            Age = CalcAge(Date);
        }

        private int CalcAge(DateTime? Date)
        {
            Age = 25;
            //TODO: Come back and enter proper logic to work out age
            return Age;
        }
    }
}

I then modified my interfaces, repositories, controllers, views etc to use this new InvoiceBL class instead of the one generated by EF.

I started using a partial class. But I have trouble with this apparently because it is in a different project. I even tried using the same namespace but nope. It is vital to me that I keep it separated by project. I want the layers to be clearly defined. So as this did not work, I opted for inheritance. I prefer this approach anyway because I am of the assumption that partial classes are a Microsoft thing and I want my philosophy to be easily transferable to any OOP language that may not have partial classes. Note also I put it back in its own namespace so it is no longer in the namespace Store.Models, but in Store.Business.

Now when I run the program, and type invoices in the url as before I get the following errors:

Invalid column name 'Discriminator'.
Invalid column name 'Age'.

When I add the [NotMapped] attribute I only get this error:

Invalid column name 'Discriminator'.

Below is all the related code starting with the EF Auto Generated model:

Store.Models:

namespace Store.Models
{
    using System;
    using System.Collections.Generic;

    public partial class Invoice
    {
        public Invoice()
        {
            this.Products = new HashSet();
        }

        public int Id { get; set; }
        public string Details { get; set; }
        public Nullable Total { get; set; }
        public Nullable Date { get; set; }

        public virtual ICollection Products { get; set; }
    }
}

Next we have interface:

namespace Store.Interfaces
{
    public interface IInvoice
    {
        void CreateInvoice(InvoiceBL invoice);
        DbSet Invoices { get; }
        void UpdateInvoice(InvoiceBL invoice);
        InvoiceBL DeleteInvoice(int invoiceId);
    }
}

Next we have the repository:

namespace Store.Repositories
{
    public class InvoiceRepository : BaseRepository, IInvoice
    {
        public void CreateInvoice(InvoiceBL invoice)
        {
            ctx.Invoices.Add(invoice);
            ctx.SaveChanges();
        }

        public DbSet Invoices
        {
            get { return ctx.Invoices; }
        }

        public void UpdateInvoice(InvoiceBL invoice)
        {
            ctx.Entry(invoice).State = EntityState.Modified;
            ctx.SaveChanges();    
        }

        public InvoiceBL DeleteInvoice(int invoiceId)
        {
            InvoiceBL invoice = ctx.Invoices.Find(invoiceId);

            if (invoice != null)
            {
                ctx.Invoices.Remove(invoice);
                ctx.SaveChanges();
            }

            return invoice;
        }
    }
}

I've shown you the business layer which both Interfaces, and Repositories layers need. So I will move on to the controller:

namespace Store.Web.Controllers
{
    public class InvoiceController : Controller
    {
        //---------------------Initialize---------------------------
        private IInvoice _invoiceRepository;
        private IProduct _productRepository;

        public InvoiceController(IInvoice invoiceRepository, IProduct productRepository)
        {
            _invoiceRepository = invoiceRepository;
            _productRepository = productRepository;
        }

        //-----------------------Create-----------------------------

        public ActionResult Create()
        {
            return View();
        }

        [HttpPost]
        [ValidateAntiForgeryToken]
        public ActionResult Create(Store.Business.InvoiceBL invoice)
        {
            if (ModelState.IsValid)
            {
                _invoiceRepository.CreateInvoice(invoice);
                return RedirectToAction("Index");
            }

            return View(invoice);
        }

        //-------------------------Read-----------------------------

        [ActionName("Index")]
        public ActionResult List()
        {
            return View(_invoiceRepository.Invoices);
        }

        public ViewResult Details(int id)
        {
            //How is this DI - If your model changes you have to alter the fields
            //addressed here.
            return View(_invoiceRepository.Invoices.FirstOrDefault(i => i.Id == id));
        }

        //-----------------------Update-----------------------------

        [ActionName("Edit")]
        public ActionResult Update(int id)
        {
            //How is this DI - If your model changes you have to alter the fields
            //addressed here.
            var invoice = _invoiceRepository.Invoices.FirstOrDefault(i => i.Id == id);

            if (invoice == null) return HttpNotFound();

            return View(invoice);
        }

        [HttpPost, ActionName("Edit")]
        [ValidateAntiForgeryToken]
        public ActionResult Update(Store.Business.InvoiceBL invoice)
        {
            if (ModelState.IsValid)
            {
                _invoiceRepository.UpdateInvoice(invoice);
                return RedirectToAction("Index");
            }
            else
            {
                return View(invoice);
            }
        }

        //-----------------------Delete-----------------------------

        public ActionResult Delete(int id = 0)
        {
            //Do you really want to always delete only the first one found?? Not cool?
            //Even though in this case, because Id is unique, it will always get the right one.
            //But what if you wanted to delete or update based on name which may not be unique.
            //The other method (Find(invoice) would be better. See products for more.
            //How is this DI - If your model changes you have to alter the fields
            //addressed here.
            var invoice = _invoiceRepository.Invoices.FirstOrDefault(i => i.Id == id);

            if (invoice == null) return HttpNotFound();

            return View(invoice);
        }

        [HttpPost, ActionName("Delete")]
        [ValidateAntiForgeryToken]
        public ActionResult DeleteConfirmed(int id)
        {
            if(_invoiceRepository.DeleteInvoice(id)!=null)
            {
                //Some code
            }
            return RedirectToAction("Index");
        }

        //-----------------------Master / Detail--------------------
    }
}

Finally the view:

@model IEnumerable

@{
    ViewBag.Title = "Index";
}

Index


    @Html.ActionLink("Create New", "Create")



@foreach (var item in Model) {
    
}


    
        
            @Html.DisplayNameFor(model => model.Age)
        
        
            @Html.DisplayNameFor(model => model.Details)
        
        
            @Html.DisplayNameFor(model => model.Total)
        
        
            @Html.DisplayNameFor(model => model.Date)
        
        
    

        
            @Html.DisplayFor(modelItem => item.Age)
        
        
            @Html.DisplayFor(modelItem => item.Details)
        
        
            @Html.DisplayFor(modelItem => item.Total)
        
        
            @Html.DisplayFor(modelItem => item.Date)
        
        
            @Html.ActionLink("Edit", "Edit", new { id=item.Id }) |
            @Html.ActionLink("Details", "Details", new { id=item.Id }) |
            @Html.ActionLink("Delete", "Delete", new { id=item.Id })

Please ignore any comments in the code as they are for my own reference and guidance.

Once again, this question is about specifically why I am getting the error mentioned and what I need to change to resolve it. I taught adding the [NotMapped] attribute would do this but it did not.

However, I am still learning about design patterns related to MVC, so if anyone has suggestions on how to structure the project better or other advice that might help, I would also welcome this.

EDIT: I forgot the NinjectControllerFactory:

namespace Store.Web.Ninject
{
    public class NinjectControllerFactory : DefaultControllerFactory
    {
        private IKernel ninjectKernel;

        public NinjectControllerFactory()
        {
            ninjectKernel = new StandardKernel();
            AddBinding();
        }

        protected override IController GetControllerInstance(RequestContext requestContext, Type controllerType)
        {
            //return base.GetControllerInstance(requestContext, controllerType);
            return controllerType == null
                ? null
                : (IController)ninjectKernel.Get(controllerType);
        }

        private void AddBinding()
        {
            //TODO FR: Step 4 - Add your interface and repository to the bindings
            ninjectKernel.Bind().To(); ;
            ninjectKernel.Bind().To(); ;
        }
    }
}

Ninject DI / ASP.Net MVC - How do I add a business layer?

Answers (1)

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