无法将类型“System.Collections.Generic.List<PetShop.Model.Item>”隐式转换为“PetShop.Model.It

  public PetShop.Model.Item GetItemById(string ItemId)
       
        {            string sql = "select item.itemid, item.name, item.listprice, product.name, item.image, product.categoryid, product.productid from item inner join product on item.productid = product.productid where item.itemid = @itemid";
            string connectionString = System.Configuration.ConfigurationManager.ConnectionStrings["ssa"].ConnectionString;
            List<PetShop.Model.Item> list = new List<PetShop.Model.Item>();
            using (SqlConnection connection = new SqlConnection(connectionString))
            {
                SqlCommand command = new SqlCommand(sql, connection);
                connection.Open();                command.Parameters.Add("@itemid", SqlDbType.NVarChar).Value = ItemId;                SqlDataReader reader = command.ExecuteReader();
                while (reader.Read())
                {
                    PetShop.Model.Item item = new PetShop.Model.Item()
                    {
                        ItemId = reader.GetString(0),
                        Name = reader.GetString(1),
                        Quantity = reader.GetInt32(2),
                        ListPrice = reader.GetDecimal(3),
                        ProductName = reader.GetString(4),
                        Image = reader.GetString(5),
                        CategoryId = reader.GetString(6),
                        ProductId = reader.GetString(7)
                    };
                    list.Add(item);                }
                return list;
            }        }