C＃Dictionary HashSet

Question

I have this Query i have to remove ORDER BY p.ID

 string query = "SELECT p.Price, p.ID, p.Name, c.Name as CategoryName, p.CategoryID, c.ID AS CategoryPK, c.ParentID,"
            + " o.ID as OrderID,o.ProductID,o.ClientCompanyID,o.Quentity"
            + " FROM Products p LEFT JOIN Categories c ON p.CategoryID=c.ID LEFT JOIN Orders o ON o.ProductID=p.ID ORDER BY p.ID";

And i have this code i should remove if clause where i have to compare last element with current element from database.

        static List<Product> GetProducts(SqlCommand command)
    {
        using (SqlDataReader reader = command.ExecuteReader())
        {

            List<Product> listProducts = new List<Product>();
            while (reader.Read())
            {

                Product product = null;
                int productId = (int)reader["ID"];

                if (listProducts.Count >= 1 && listProducts[listProducts.Count - 1].ID == productId)
                {
                    product = listProducts[listProducts.Count - 1];
                }

                if (product == null)
                {
                    product = new Product();

                    product.ID = productId;

                    product.Name = (!reader.IsDBNull(reader.GetOrdinal("Name")) ? (string)reader["Name"] : null);
                    product.Price = reader.GetDecimal(reader.GetOrdinal("Price"));
                    product.CategoryID = reader.GetInt32(reader.GetOrdinal("CategoryID"));
                    Category newCat = new Category();
                    newCat.ID = reader.GetInt32(reader.GetOrdinal("CategoryPK"));
                    newCat.CategoryName = reader.GetString(reader.GetOrdinal("CategoryName"));
                    newCat.Parent = (!reader.IsDBNull(reader.GetOrdinal("ParentID")) ? reader.GetInt32(reader.GetOrdinal("ParentID")) : 0);
                    product.Category = newCat;

                }

                Order order = new Order();
                order.ID = (!reader.IsDBNull(reader.GetOrdinal("OrderID")) ? (int?)reader["OrderID"] : null);
                order.ClientCompanyID = (!reader.IsDBNull(reader.GetOrdinal("ClientCompanyID")) ? (int?)reader["ClientCompanyID"] : null);
                order.ProductID = (!reader.IsDBNull(reader.GetOrdinal("ProductID")) ? (int?)reader["ProductID"] : null);
                order.Quentity = (!reader.IsDBNull(reader.GetOrdinal("Quentity")) ? (int?)reader["Quentity"] : null);

                product.Orders.Add(order);
                listProducts.Add(product);
            }
            reader.Close();
            listProducts = listProducts.Distinct().ToList();
            return listProducts;
        }
    }

I have to remove Order By in query and then use Dictionary in method to get this data from database but i am new to Dictionary. Can someone help me how to make it. Thanks!

Answer 1

If you need just to return Dictionary< int,Product > where key is product ID, then modify your return to:

   return listProducts.GroupBy(x => x.ID).
   ToDictionary(y => y.Key, z => z.ToList());