NullReferenceException was unhandled asp.net entity framework

Question

I'm new to asp.net mvc and I'm doing this exercise for myself. I created an edmx from Northwind Database. I created a controller:

 public ActionResult Index(int id)
    {
        var model = new IndexViewModel();
        using (var db = new ProductDB())
        {
            model.Products = from p in db.Products
                             orderby p.ProductName

                             select new IndexViewModel.InfoProduct
                             {
                                 ProductName = p.ProductName,
                                 QuantityPerUnit = p.QuantityPerUnit,
                                 UnitPrice = p.UnitPrice
                             };
        }
        return View();
    }

...the view:

    @model aspTest.Models.IndexViewModel
@{
    Layout = null;
}

...

    <div> <ul>
        @foreach (var p in Model.Products){
    <li>@p.ProductName</li>
}
        </ul>
    </div>

...and the ViewModel:

public class IndexViewModel
{
    public IEnumerable<InfoProduct> Products { get; set; }

    public class InfoProduct
    {            
        public string ProductName { get; set; }
    }

}

But this error keeps on appearing in this part: @foreach (var p in Model.Products){

@p.ProductName

Sorry, I know this might be noobish to most of you.

user3021830 · Accepted Answer · 2015-02-19 10:01:41Z

5

You are declaring in your model that it will work with the IndexViewModel class as:

@model aspTest.Models.IndexViewModel

but you are sending nothing to the View from Controller as :

return View();

Try using:

return View(model);

The error is quite true, you are trying to iterate on properties (Products) of an object (IndexViewModel) which you don't provide.

answered Feb 19, 2015 at 10:01

user3021830

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5 Comments

Caloyski Over a year ago

That was fast! Thanks! But now another error in the same line appeared... An exception of type 'System.ObjectDisposedException' occurred in EntityFramework.dll but was not handled in user code Additional information: The ObjectContext instance has been disposed and can no longer be used for operations that require a connection.

user3021830 Over a year ago

Can you please try to put return View(model); within the scope of using?

user3559349 Over a year ago

You need to materialize your query, for example .ToList() before you pass it to the view

user3021830 Over a year ago

Oh yes, Stephen is quite right. Just writing linq prepares everything about the query but does not actually run and fetch data unless you intent to. You can use ToList(), ToArray() etc as Stephen suggested.

Caloyski Over a year ago

Thanks guys, have a blessed day!

Marco · Accepted Answer · 2015-02-19 10:14:55Z

Besides the fact that you return no ViewModel to your view and shout use return View(model); there is something else fishy with your code:

public class InfoProduct
{            
    public string ProductName { get; set; }
}

Your class InfoProduct only contains a Productname, yet you also assign a Quantity and Price property in your select clause, this won't compile.

model.Products = from p in db.Products
                 orderby p.ProductName
                 select new IndexViewModel.InfoProduct
                 {
                      ProductName = p.ProductName,
                 };

Lastly, materialize your data using .ToList()

public ActionResult Index(int id)
{
    var model = new IndexViewModel();
    using (var db = new ProductDB())
    {
       model.Products = (from p in db.Products
                         orderby p.ProductName
                         select new IndexViewModel.InfoProduct
                         {
                             ProductName = p.ProductName,
                         }).ToList();
       return View(model);
    }

}

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