method that adds values together if ID is the same

Question

Hello I am currently trying to figure out how to add values together if their item id's are the same in my SQL database. Here is a view of my database

As you can see two of the values have the same "ItemID" with a value of 117. I want my method to return the combined quantities of the two values so in this case I would want it to return the value "14"

Here is my method inside my model that pulls the item quantity

  public int Available(Item i)
        {

            OffSiteItemDetails d = ItemDetails.Where(x => x.itemID == i.ID).FirstOrDefault();
            if (d == null)
                return 0;
            return d.qty;
        }

but just not sure how to combine the values when there is more than one value with the same ID

Answer 1

public int Available(Item i)
{

    List<OffSiteItemDetails> d = ItemDetails.Where(x => x.itemID == i.ID).ToList();
    if (d == null || d.Count < 1)
        return 0;

    return d.Sum(x => x.qty);
}