The X property on Y could not be set to a 'Decimal' value. You must set this property to a non-null value of type 'Single'

Question

So I have this fairly compelx LINQ query:

        // This query will get the top 10 items sold. 
        IEnumerable<IGrouping<Item, ItemSale>> results = (
            from x in database.ItemSales
            where shiftIDs.Contains(x.shiftID)
            group x by x.item into itemSalesGroup
            orderby itemSalesGroup.Sum(y => y.SalesValue) descending
            select itemSalesGroup
        ).Take(10);

And it's crashing on y.SalesValue saying it could not be set to a decimal value. How do I fix this? I have tried the following:

        orderby itemGroup.Sum(y => (float?)y.SalesValue) ?? 0f descending
        orderby itemGroup.Sum(y => (float?)y.SalesValue ?? 0f) descending

Here are the relevent Entity-Framework Code First definition:

[Table("ItemSales")]
public class ItemSale {
    public int ID { get; set; }
    [Column("ItemID")]
    public int itemID { get; set; }
    [ForeignKey("itemID")]
    public Item item { get; set; }
    [Column("Shifts_ID")]
    public int shiftID { get; set; }
    [ForeignKey("shiftID")]
    public Shift shift { get; set; }
    ...
    public float SalesValue { get; set; }
}

Answer 1

The expression parameter for Enumerable.Sum cannot return a float. Since it can work with singles, decimals, doubles, etc., it doesn't know which to implicitly cast it to. You have to explicitly cast it.

Try this

 orderby itemSalesGroup.Sum(y => (single) (y.SalesValue)) descending

Answer 2

In your entity you have Decimal type and you are returning single type from SQL. Update your SQL query (better) or your entity.