Question

I have created an entity data model from my database. however in certain areas of the application i need to pass two models. thus i create a third model which has as properties the objects of each required model.

In the scenario, i want to use one model just to show some data to the user and the other is to be populated by the user using form elements. therefore, i create a constructor in my custom model to populate it. here’s the code:

THE CUSTOM MODEL

public class ordersModel
{
    public ordersModel(order or)
    {
        this.prods = new order_products();
        this.new_order = new order();
        this.new_order.customer_id = or.customer_id;
        this.new_order.my_id = or.my_id;
        this.new_order.my_order_id = or.my_order_id;
        this.new_order.order_date = or.order_date;
        this.new_order.order_status_id = or.order_status_id;
    }
    public order new_order { get; set; }
    public order_products prods { get; set; }
}

IT IS USED IN THE CONTROLLER AS FOLLOWS:

public ActionResult Create()
    {
        order or = new order();
        // Store logged-in user's company id in Session
        //or.my_id = Session["my_id"].ToString();
        //do something to allow user to select customer, maybe use ajax
        or.customer_id = "123";
        or.order_amount = 0;
        or.my_id = "74973f59-1f6c-4f4c-b013-809fa607cad5";
        // display date picker to select date
        or.order_date = DateTime.Now.Date;
        // fetch statuses from database and show in select list box
        or.order_status_id = 1;
        return View(or);
    } 

    //
    // POST: /Orders/Create

    [HttpPost]
    public ActionResult Create(order or)
    {
        using (invoicrEntities db = new invoicrEntities())
        {
            var temp = db.last_order_number.SingleOrDefault(p => p.my_id == or.my_id);
            if (temp != null)
            {
                or.my_order_id = temp.my_order_id + 1;
                if (ModelState.IsValid)
                {
                    ordersModel ord = new ordersModel(or);

                    db.orders.AddObject(or);
                    temp.my_order_id = temp.my_order_id + 1;
                    //TempData["my_order_id"] = or.my_order_id;
                    db.SaveChanges();
                    return RedirectToAction("AddProducts", ord);
                    //return RedirectToAction("AddProducts", new { id = or.my_order_id });
                }
                return View(or);
            }
            return RedirectToAction("someErrorPageDueToCreateOrder");
        }
    }

    public ActionResult AddProducts()
    {
        using (invoicrEntities db = new invoicrEntities())
        {
            //string my_id = TempData["my_id"].ToString();
            //string my_order_id = TempData["my_order_id"].ToString();

            string my_id = "74973f59-1f6c-4f4c-b013-809fa607cad5";
            int my_order_id = 1;
            //Int64 my_order_id = Convert.ToInt64(RouteData.Values["order_id"]);

            // Display this list in the view
            var prods = db.order_products.Where(p => p.my_id == my_id).Where(p => p.my_order_id == my_order_id).ToList();

            var or = db.orders.Where(p => p.my_id == my_id).Where(p => p.my_order_id == my_order_id).ToList();
            if (or.Count == 1)
            {
                //ViewData["name"] = "sameer";
                ViewData["products_in_list"] = prods;
                ViewData["order"] = or[0];
                return View();
            }
            return RedirectToAction("someErrorPageDueToAddProducts");
        }
    }

    [HttpPost]
    public ActionResult AddProducts(order_products prod)
    {
        prod.my_id = "74973f59-1f6c-4f4c-b013-809fa607cad5";
        // find a way to get the my_order_id
        prod.my_order_id = 1;
        return View();
    }

THIS ALL WORKS OUT WELL, UNTIL IN THE “ADDPRODUCTS” VIEW:

<%@ Page Title="" Language="C#" MasterPageFile="~/Views/Shared/Site.Master" Inherits="System.Web.Mvc.ViewPage<invoicr.Models.ordersModel>" %>

AddProducts

<h2>AddProducts</h2>
<%: Model.new_order.my_id %>

the above statement gives an error

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

what am i doing wrong here?

Answer 1

You seem to be passing the wrong model when redisplaying your Create view.

Try passing the ord instance which is of type ordersModel and which is what your view is strongly typed to:

public ActionResult Create(order or)
{
    using (invoicrEntities db = new invoicrEntities())
    {
        var temp = db.last_order_number.SingleOrDefault(p => p.my_id == or.my_id);
        if (temp != null)
        {
            or.my_order_id = temp.my_order_id + 1;
            ordersModel ord = new ordersModel(or);
            if (ModelState.IsValid)
            {
                db.orders.AddObject(or);
                temp.my_order_id = temp.my_order_id + 1;
                db.SaveChanges();
                return RedirectToAction("AddProducts", ord);
            }
            return View(ord);
        }
        return RedirectToAction("someErrorPageDueToCreateOrder");
    }
}

---

UPDATE:

Now that you have shown your AddProducts action you are not passing any model to the view although your view expects an ordersModel instance. So don’t just return View();. You need to pass an instance of ordersModel:

if (or.Count == 1)
{
    ViewData["products_in_list"] = prods;
    ViewData["order"] = or[0];
    ordersModel ord = new ordersModel(or[0]);
    return View(ord);
}