项目需求：

某学校订单截止操作时间的上一个月最后一天晚上23：59：59 为止所有支付的订单统计；

代码：

---

        /// <summary>

        /// 通过学校和截止时间得到订单

        /// </summary>

        /// <param name="pageIndex">页个数</param>

        /// <param name="pageSize">页面积</param>

        /// <param name="schoolId">学校ID</param>

        /// <param name="orderSettlementEndTime">截止时间</param>

        /// <returns></returns>

        public PagedList<Order> GetOrderBySchoolAndEndTime(int pageIndex,int pageSize,Guid? schoolId, DateTime? orderSettlementEndTime)

        {

            var query = this.Table;

            if (schoolId.HasValue)

            {

                query = query.Where(x => x.SchoolId == schoolId);

            }

            if (orderSettlementEndTime.HasValue)

            {

                //本月的最后一天

                var endMonth = DateTime.Parse(

                    orderSettlementEndTime.Value.AddDays(1 - orderSettlementEndTime.Value.Day)

                        .AddMonths(1)

                        .AddDays(-1)

                        .ToString());

                //上月的最后一天

                var startMonth =

                    DateTime.Parse(

                        orderSettlementEndTime.Value.AddDays(1 - orderSettlementEndTime.Value.Day)

                        .AddSeconds(-1).ToString());

                query = query.Where(x => x.CreateTime >= startMonth&&x.CreateTime<endMonth);

            }

            return query.Where(x => x.PaymentState == PaymentState.支付完成)

                .OrderBy(x=>x.Id)

                .ToPagedList(pageIndex,pageSize);

        }

图片：

利用DateTime.Parse();将string类型的时间转换为datetime类型，我们看一下后面的代码，是将时间手动的设置为我们需要的时间。

                DateTime today12hours = DateTime.Parse(DateTime.Now.ToString("yyyy-MM-dd 12:00:00"));

这样我们设置了值。

封装取时间的方法

        /// <summary>

        /// 某月的最后一天

        /// </summary>

        /// <param name="datetime"></param>

        /// <returns></returns>

        public DateTime FirstDayOfMonth(DateTime datetime)

        {

            return datetime.AddDays(1 - datetime.Day).AddMonths(1).AddDays(-1);

        }

        /// <summary>

        /// 前一月的最后一天

        /// </summary>

        /// <param name="datetime"></param>

        /// <returns></returns>

        public DateTime LastDayOfMonth(DateTime datetime)

        {

            return datetime.AddDays(1 - datetime.Day).AddSeconds(-1);

        }

        /// <summary>

        /// 某月的第一天

        /// </summary>

        /// <param name="datetime"></param>

        /// <returns></returns>

        public DateTime FirstDayOfMonthMethod(DateTime datetime)

        {

            return datetime.AddDays(1 - datetime.Day);

        }

        /// <summary>

        /// 上一月的第一天

        /// </summary>

        /// <param name="datetime"></param>

        /// <returns></returns>

        public DateTime FirstDayOfUpMouth(DateTime datetime)

        {

            return datetime.AddDays(1 - datetime.Day).AddMonths(-1);

        }

        /// <summary>

        /// 取得上个月的最后一天

        /// </summary>

        /// <param name="datetime"></param>

        /// <returns></returns>

        public DateTime LastDayOfOnMouth(DateTime datetime)

        {

            return datetime.AddDays(1 - datetime.Day).AddDays(-1);

        }