使用Expression进行动态排序分页

Expression动态查询、分页

Expression，表达式树，以lamda表达式创建，就以表达式目录树的形式将强类型的lambda表达式标识为数据结构。

排序

 /// <summary>
        /// 根据条件排序和查询
        /// </summary>
        /// <typeparam name="TKey">排序字段类型</typeparam>
        /// <param name="whereLambda">查询条件 lambda表达式</param>
        /// <param name="orderLambda">排序条件 lambda表达式</param>
        /// <returns></returns>
        public static  IEnumerable<Customers> GetListBy<TKey>(Expression<Func<Customers, bool>> whereLambda, Expression<Func<Customers, TKey>> orderLambda)
        {
            using (NorthwindEntities db = new NorthwindEntities())
            {
                return db.Customers.Where(whereLambda).OrderBy(orderLambda).ToList();
            }
        }

常见分页

 /// <summary>
        /// 分页查询
        /// </summary>
        /// <param name="pageIndex">页码</param>
        /// <param name="pageSize">页容量</param>
        /// <param name="whereLambda">条件 lambda表达式</param>
        /// <param name="orderBy">排序 lambda表达式</param>
        /// <returns></returns>
        public static List<Customers> GetPagedList<TKey>(int pageIndex, int pageSize, Expression<Func<Customers, bool>> whereLambda,
                    Expression<Func<Customers, TKey>> orderBy)
        {
            using (NorthwindEntities db = new NorthwindEntities())
            {
                // 分页时一定注意： Skip 之前一定要 OrderBy
                return db.Customers.Where(whereLambda).OrderBy(orderBy).Skip((pageIndex - 1) * pageSize).Take(pageSize).ToList();
            }
        }

 调用：

 var a = GetListBy<string>((p)=> p.CustomerID == "11", (q) => q.ContactName);

  IQueryable<Orders> or = db.Orders.Where(u=>u.CustomerID=="11").Take(1);
                List<Orders> aa = or.ToList();