EF can't get the reference entity of navigation property of an entity

Question

This is my model classes

public class Serve
{
    public int Id { get; set; }
    public Table Table { get; set; }
    public bool IsFinished { get; set; }
    public decimal TotalMoney { get; set; }
    public virtual ICollection<Order> Orders { get; set; }
}
public class Order
{
    public int Id { get; set; }
    public Item Item { get; set; }
    public int Numbers { get; set; }
    public bool IsCheifReceived { get; set; }
    public bool IsCheifCooked { get; set; }
    public Serve Serve { get; set; }

    public Order()
    {
        IsCheifCooked = IsCheifReceived = false;
    }
}

public class Item
{
    public int Id { get; set; }    
    public string Name { get; set; }    
    public string Unit { get; set; }
    public decimal Price { get; set; }    
    public Category Category { get; set; }    
    public bool IsNeedToNotifyChief { get; set; }
}

I want to sum the Number and total money of Orders grouped by same Item (This is the Menu Item of the restaurant).

This is the LINQ query.

var serving = db.Serves
                    .Where(m => m.Table.Id == table.Id)
                    .Where(m => m.IsFinished == false)
                    .OrderByDescending(m => m.Id)
                    .FirstOrDefault();

var groupedOrder = serving.Orders
                        .OrderByDescending(m => m.Id)
                        .GroupBy(m => m.Item)
                        .Select(g => new
                        {
                            Item = g.Key,
                            Numbers = g.Sum(ri => ri.Numbers)
                        }).ToList();

But in this case, in .GroupBy(m => m.Item) the m.Item is null , and it grouped all the Orders to one group. (I know the problem is the m.Item is not loaded in this Query)

Here, I don't know how to make the m.Item is loaded in this LINQ Query. Please help me to do this.

PS: I use Entity Framework 6

Answer 1

I think the variable serving is list of some objects, not a query. If I'm right, you should to include items when you getting serving from DB. It will be look like code below:

var serving = db.Serves
                 .Include(x => x.Orders)
                 .Include(x => x.Orders.Select(x => x.Item)) //here you'll get your items
                 .Where(m => m.Table.Id == ta && m.IsFinished == false)
                 .OrderByDescending(m => m.Id)
                 .FirstOfDefault();

//and after that your code should work correctly

if(serving != null) //don't forget check it, if you use FirstOfDefault()
{
   var groupedOrder = serving.Orders
            .OrderByDescending(m => m.Id)
            .GroupBy(m => m.Item) 
            .Select(g => new
            {
                Item = g.Key,
                Numbers = g.Sum(ri => ri.Numbers)
            }).ToList();
}