Based on class that has no key defined mvc5

问题:

I try to add view from this controller . I only need this view to show data not for insert or update or delete

public ActionResult Index()
{
    var CartObj = ShoppingCart.GetCart(this.HttpContext);

    var classshop = new New
    {
        CartItems = CartObj.GetCartItems(),
        CartTotal = CartObj.GetSum()
    };

    return View(classshop);
}

namespace MusicStore.Models
{
    public class ShoppingCart
    {
        MusicStoreEntities dbo = new MusicStoreEntities();
        string ShoppingCartID { get; set; }

        public const string CartSessionKey = "CartId";
        public static ShoppingCart GetCart(HttpContextBase Context)
        {
            var cart = new ShoppingCart();
            cart.ShoppingCartID = cart.GetCardId(Context);
            return cart;
        }
        public static ShoppingCart GetCart(Controller controller)
        {
            return GetCart(controller.HttpContext);
        }

        public  List<Cart> GetCartItems()
        {
            return dbo.Carts.Where(a => a.CartId == ShoppingCartID).ToList();
        }

        public decimal? GetSum()
        {
            decimal? Sum = (from items in dbo.Carts
                         where items.CartId == ShoppingCartID
                         select (int)items.Count * items.album.Price).Sum();
            return Sum ?? decimal.Zero;
        }
    }
}

and then I got this error:

there was an error running the selected code generator: 'unable to retrieve metadata for 'Musicstore.Model.new' one or more validation error were detected during model generation musicstore,models.New :entity type'New' has no key defined . define the key of entityType

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace MusicStore.Models
{
    public class New
    {
        public List<Cart> CartItems { get; set; }
        public decimal? CartTotal { get; set; }

    }
}

回答1:

There are two options here. First, if this class is mapped to a table in your database, every model in entity framework requires a primary key. Add this into your model:

[Key]
public int Id { get; set; }

This creates a new property called Id and the [Key] attribute makes it a primary key. Technically you don't need the attribute as EF will pick up Id property and use it as a key, but I prefer to be explicit.

Alternatively, if you don't want this class to be a table in your database, add the NotMapped attribute to the class like this:

[NotMapped]
public class New
{
    public List<Cart> CartItems { get; set; }
    public decimal? CartTotal { get; set; }

}

回答2:

I know this is old, but I just ran across this issue.

What happen is when I created a class, CreateEmployeeViewModel, inside the Models folder Visual Studio "smartly" put a line in my DB Context class

public System.Data.Entity.DbSet<eManager.Web.Models.CreateEmployeeViewModel>
       CreateEmployeeViewModels { get; set; }

So a table was created on the next update-migration. Removing this line removed the requirement for a key field.

Note: You may also have to add the line AutomaticMigrationDataLossAllowed = true; to your DBMigrationConfiguration Class if the table was created.