VS.2010.C#.LINQ 学习(三)-not in、排序、分页

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本文介绍如何使用LINQ实现SQL中的IN和NOT IN操作，并展示了排序、分页等实用查询技巧。

1.SQL中的in和not in语法对应的LINQ写法

            List<testInfo> listAll = new List<testInfo>();
            listAll.Add(new testInfo() { id = 1, name = "11", test = "111" });
            listAll.Add(new testInfo() { id = 2, name = "22", test = "222" });
            listAll.Add(new testInfo() { id = 3, name = "33", test = "333" });
            listAll.Add(new testInfo() { id = 4, name = "33", test = "333" });

            List<testInfo> listFind = new List<testInfo>();
            listFind.Add(new testInfo() { id = 1, name = "44", test = "111" });
            listFind.Add(new testInfo() { id = 2, name = "22", test = "222" });
            listFind.Add(new testInfo() { id = 3, name = "33", test = "333" });
            listFind.Add(new testInfo() { id = 4, name = "55", test = "333" });
            //SQL中的in和not in语法对应的LINQ写法
            //相当于查询语句：select * from listAll p where p.name not in(select f.name from listFind)
            var a = (from p in listAll
                     where !(from f in listFind select f.name).Contains(p.name)
                     select p).ToList();

2.排序

                    list = (from p in list
                         orderby p.shipname ascending
                         select p).ToList();

3.分页查询

int pageSize = 20;//每页记录数
int pageIndex=1;//当前页
        //分页
       list = (from p in list
             select p).Skip(pageSize * (pageIndex - 1)).Take(pageSize).ToList();

4.分页查询2

        /// <summary>
        /// 计算列表可以分多少页 (此方法可以自己改良,赶时间只能写这么烂的代码了)
        /// </summary>
        /// <param name="dataList">List</param>
        /// <returns>总页数</returns>
        private int GetListPageCount(List<string> dataList)
        {
            int pageCount = 1;
            int pageSize = 1000;//每页一千条  
            int rowCount = dataList.Count; 
            decimal temp = (decimal)rowCount / (decimal)pageSize;
            string[] arry1 = temp.ToString().Split('.');
            int temp2 = 0, temp3 = 0;
            Int32.TryParse(arry1[0], out temp2);
            if (arry1.Length > 1)
            {
                Int32.TryParse(arry1[1], out temp3);
            }
            if (temp2 > 1)
            {
                pageCount = temp2;
            }
            if (temp3 > 0)
            {
                pageCount = temp2 + 1;
            }

            return pageCount;
        }
        /// <summary>
        /// 返回List某页数据
        /// </summary>
        /// <param name="dataList">List</param>
        /// <param name="pageIndex">某页</param>
        /// <returns>返回某页数据</returns>
        private List<string> GetListByPage(List<string> dataList, int pageIndex)
        {
            //每页多少记录
            int pageSize = 1000;
            //分页  
            var list = (from p in dataList
                        select p).Skip(pageSize * (pageIndex - 1)).Take(pageSize).ToList();
            return list;
        }
        
        
        //------------------------使用-----------------------------------
        {
      int pageCount = 0;
      pageCount = GetListPageCount(allDataList);   //allDataList是需要分页的list
      for (int i = 1; i <= pageCount; i++)
      {
          var pageDataList = GetListByPage(allDataList, i);//第i页数据
          //处理方法()
      }
      }
      //-------------------------------------------