接口与继承，并处理业务关系 评论一下内容优点和缺点，如何做更好~

using System;
using System.Collections.Generic;
using System.Data;
using System.Linq;
using System.Web;
using GuoTBManage.Models;
namespace GuoTBManage.Cor
{
    /// <summary>
    /// 订单处理接口
    /// </summary>
    public interface ITrade
    {
        void UpdateTradeByTid(string Tid);
        bool CheckTrade(string Tid);
        void InsertTrade(TB_Trade trade);
        TB_Trade GetTrade(string Tid);
    }
    /// <summary>
    /// 订单处理实现
    /// </summary>
    public class Trade : ITrade
    {
        /// <summary>
        /// 更新订单信息
        /// </summary>
        /// <param name="Tid"></param>
        public void UpdateTradeByTid(string Tid)
        {
            TB_Trade trade = GetTrade(Tid);
            if (trade == null)
            {
                trade = new TB_Trade();
                InsertTrade(trade);
            }
            else
            {
                using (GuoTBManageEntities context = new GuoTBManageEntities())
                {
                    context.Entry(trade).State = EntityState.Modified;
                    context.SaveChanges();
                }
            }
        }
        /// <summary>
        /// 检测有效订单
        /// </summary>
        /// <param name="Tid">订单号</param>
        /// <returns>返回真假</returns>
        public bool CheckTrade(string Tid)
        {
            TB_Trade trade=GetTrade(Tid);
            return trade == null ? false : true;
        }
        /// <summary>
        /// 添加订单信息
        /// </summary>
        /// <param name="trade">订单实体</param>
        public void InsertTrade(TB_Trade trade)
        {
            try
            {
                using (GuoTBManageEntities context = new GuoTBManageEntities())
                {
                    context.TB_Trades.Add(trade);
                    context.SaveChanges();
                }
            }
            catch {
　　　　　　　　　throw new ArgumentNullException("添加订单信息失败~");
            }
            finally {
            }
        }
        /// <summary>
        /// 获取实体订单
        /// </summary>
        /// <param name="Tid">订单编号</param>
        /// <returns>返回实体订单</returns>
        public TB_Trade GetTrade(string Tid)
        {
            using (GuoTBManageEntities context = new GuoTBManageEntities())
            {
                return context.TB_Trades.SingleOrDefault(U => U.tid == Tid);
            }
        }
    }
}