asp.net MVC + EF , Linq的基本用法

 public ActionResult Index()
        {
            NewsEntities news = new NewsEntities();

            //select * from NewsInfo

            #region 排序
            var query = from s in news.NewsInfo
                        orderby s.ID descending   //ascending
                        select new { id = s.ID, name = s.Name, auter = s.Auter };   //构造属性

            foreach (var item in query)
            {
                int id = item.id;
                string name = item.name;
            }
            #endregion

            #region where条件  + top
            //var query1 = from s in news.NewsInfo
            //            where s.ID >= 1 && s.ID <= 6
            //            select s;

            var query1 = (from s in news.NewsInfo
                          where s.Name.StartsWith("啊")  //EndsWith :  name like ‘%啊‘ ,Contains : name like ‘%啊%‘ , StartsWith : name like ‘啊%‘
                          select s).Take(3);   //take() 类似top

            foreach (var item in query1)
            {
                int id = item.ID;
                string name = item.Name;
            }
            #endregion

            #region 函数
            var query2 = from s in news.NewsInfo
                         group s by new { s.ID, s.Time } into tab
                         select tab;

            //int? sum = query3.Sum(f => f.Key.ID);
            //System.DateTime? maxid = query3.Max(f => f.Key.Time);

            foreach (var item in query2)
            {
                var id = item.Key.ID;
                var time = item.Key.Time;

                //统计一组数据记录数
                int count = item.Count();

                //计算一组的平均ID
                double? avg = item.Average(f => f.ID);

                //计算ID之和
                int? sum = item.Sum(f => f.ID);

                //统计当前最大 最小的ID数
                int? maxid = item.Max(f => f.ID);
                int? minid = item.Min(f => f.ID);
            }
            #endregion

            #region  skip(跳过指定前几行) + take(再获取前几行)

            var query3 = (from s in news.NewsInfo
                          orderby s.ID ascending
                          select s).Skip(2).Take(3);   //take() 类似top

            foreach (var item in query3)
            {
                int id = item.ID;
                string name = item.Name;
            }
            #endregion

            #region linq 分页操作

            //当前页码
            int pageindex = 1;
            //每页数量
            int pagesize = 2;

            var list = (from s in news.NewsInfo
                        orderby s.ID ascending
                        select s).Skip((pageindex - 1) * pagesize).Take(pagesize);

            #endregion

            #region  链表查询(查询数据里的所有男女性别 并输出男女性别数量)

            var list1 = from ss in
                            (
                                from s in news.NewsInfo
                                join g in news.GTable on s.ID equals g.ID
                                select new
                                {
                                    id = s.ID,
                                    name = s.Name,
                                    gsex = g.Sex
                                }
                            )
                        group ss by ss.gsex into tab
                        select tab;
            foreach (var item in list1)
            {
                var Class = item.Key;
                var count = item.Count();
            }

            #endregion

            #region  子表查询(用b表的ID查询a表的name列)

            var zi = from b in news.GTable
                     select new
                     {
                         id = b.ID,
                         name = (
                             from a in news.NewsInfo
                             where b.ID == a.ID
                             select a.Name
                         ).FirstOrDefault()
                     };
            foreach (var item in zi)
            {
                var name = item.id;
                var gname = item.name;
            }
            #endregion

            return View();
        }

原文地址：https://www.cnblogs.com/lbx6935/p/9812642.html