The entity cannot be constructed in a LINQ to Entities query

Question

There is an entity type called Product that is generated by entity framework. I have written this query

public IQueryable GetProdu         


        

Answer 1

It won't let you map back onto Product since that is your table you are querying. You need an anonymous function, then you can add it to a ViewModel, and add each ViewModel to a List and return these. It's a slight digression, but I include caveats about handling nullable dates because these are a pain in the behind to deal with, just in case you have any. This is how I handled it.

Hopefully you have a ProductViewModel:

public class ProductViewModel
{
    [Key]
    public string ID { get; set; }
    public string Name { get; set; }
}

I have dependency injection/repository framework where I call a function to grab my data. Using your post as an example, in your Controller function call, it would look like this:

int categoryID = 1;
var prods = repository.GetProducts(categoryID);

In the repository class:

public IEnumerable GetProducts(int categoryID)
{
   List lstPVM = new List();

   var anonymousObjResult = from p in db.Products
                            where p.CategoryID == categoryID 
                            select new
                            {
                                CatID = p.CategoryID,
                                Name = p.Name
                            };

        // NOTE: If you have any dates that are nullable and null, you'll need to
        // take care of that:  ClosedDate = (DateTime?)p.ClosedDate ?? DateTime.Now

        // If you want a particular date, you have to define a DateTime variable,
        // assign your value to it, then replace DateTime.Now with that variable. You
        // cannot call a DateTime.Parse there, unfortunately. 
        // Using 
        //    new Date("1","1","1800"); 
        // works, though. (I add a particular date so I can edit it out later.)

        // I do this foreach below so I can return a List. 
        // You could do: return anonymousObjResult.ToList(); here
        // but it's not as clean and is an anonymous type instead of defined
        // by a ViewModel where you can control the individual field types

        foreach (var a in anonymousObjResult)
        {                
            ProductViewModel pvm = new ProductViewModel();
            pvm.ID = a.CatID;  
            pvm.Name = a.Name;
            lstPVM.Add(rvm);
        }

        // Obviously you will just have ONE item there, but I built it 
        // like this so you could bring back the whole table, if you wanted
        // to remove your Where clause, above.

        return lstPVM;
    }

Back in the controller, you do:

 List lstProd = new List();

 if (prods != null) 
 {
    // For setting the dates back to nulls, I'm looking for this value:
    // DateTime stdDate = DateTime.Parse("01/01/1800");

    foreach (var a in prods)
    {
        ProductViewModel o_prod = new ReportViewModel();
        o_prod.ID = a.ID;
        o_prod.Name = a.Name;
       // o_prod.ClosedDate = a.ClosedDate == stdDate ? null : a.ClosedDate;
        lstProd.Add(o_prod);
    }
}
return View(lstProd);  // use this in your View as:   @model IEnumerable