public class Operation:IDisposable    {        private EFContext ef {            get { return new EFContext(); }            }        /// <summary>        /// 添加一个实体对象        /// </summary>        /// <typeparam name="T"></typeparam>        /// <param name="t"></param>        public void Add<T>(T t) where T:class        {            ef.Set<T>().Add(t);            ef.SaveChanges();        }        /// <summary>        /// 释放掉EFContext        /// </summary>        public void Dispose()        {            if (ef != null) {                ef.Dispose();            }        }        /// <summary>        /// 获取实体对象的条数        /// </summary>        /// <typeparam name="T">实体对象类</typeparam>        /// <param name="t">对象实例</param>        /// <returns></returns>        public int Count<T>(T t) where T : class         {           return ef.Set<T>().Count<T>();        }        /// <summary>        /// 获取实体对象的所有集合        /// </summary>        /// <typeparam name="T">实体类</typeparam>        /// <returns></returns>        public IQueryable<T> GetList<T>() where T : class         {          return ef.Set<T>().AsQueryable<T>();        }       /// <summary>        /// 获取实体对象的所有集合       /// </summary>        /// <typeparam name="T">实体类</typeparam>       /// <param name="start">开始</param>       /// <param name="count">行数size</param>       /// <returns></returns>        public IQueryable<T> GetLsit<T>(int start, int count)where T:class         {          return  ef.Set<T>().Skip(start).Take(count);        }        /// <summary>        /// 根据条件返回一个唯一的实体对象        /// </summary>        /// <typeparam name="T">实体类</typeparam>        /// <param name="p">表达式</param>        /// <returns></returns>        public T Get<T>(System.Linq.Expressions.Expression<Func<T, bool>> p) where T : class         {           return ef.Set<T>().SingleOrDefault<T>(p);        }        /// <summary>        /// 删除指定的实体对象        /// </summary>        /// <typeparam name="T">实体类</typeparam>        /// <param name="t">删除的实例对象</param>        /// <returns>返回这个实例对象</returns>        public T Delete<T>(T t) where T : class         {            ef.Set<T>().Remove(t);            ef.SaveChanges();            return t;        }        /// <summary>        /// 更新一个实体对象        /// </summary>        /// <typeparam name="T">实体类</typeparam>        /// <param name="t">更新的实例对象</param>        /// <returns>返回这个实例对象</returns>        public T UpDate<T>(T t) where T : class         {           ef.Entry<T>(t).State = System.Data.Entity.EntityState.Detached;           ef.SaveChanges();           return t;         }    }