NullReferenceException未处理asp.net实体框架

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.

Answer 1

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.

Answer 2

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);
    }

}