Linq使用之标准运算符方法

  #region linq的标准查询运算符（即lambda方式） 注：C#不支持标准查询运算符中带有整形参数（索引）的重载

            // 1、标准查询运算符之筛选方法——where
            //IQueryable<Student> stu1=db.Student.Where(s => s.Ssex == "男");
            //GridView1.DataSource = stu1;
            //GridView1.DataBind();           


            // 2、标准查询运算符之s投影方法——select

            //var stu2 =db.Student.Select(s => new {s.Sno,s.Sname,s.Sage}); //这叫匿名对象
            //GridView2.DataSource = stu2;
            //GridView2.DataBind();           


            //3、标准查询运算符之排序方法—— order
            //升序排序
            var stu3 = db.Student.OrderBy(s => s.Sage);
            GridView1.DataSource = stu3;
            GridView1.DataBind();

            //降序排序之多条件排序
            var stu4 = db.Student.OrderByDescending(s => s.Sage).ThenByDescending(s=>s.Sno);
            GridView2.DataSource = stu4;
            GridView2.DataBind();

　　　　//备注：OrderBy()和OrderDescendingBy（）方法不会改变原列表 而是返回排序后的列表 这点是和Sort的不同之处之一。

　　　　//pers.Sort((p1, p2) => p1.Age - p2.Age); //按照Age升序排序

            //4、标准运算符之连接集合—— Join

　　　　// 第一个参数：要连接的对象（B）第二个参数：A对象及A对象用来连接的字段；第三个参数：B对象及B对象用来连接的字段；第四个参数：A,B=>返回的对象
            var stu5 = db.Student.Join(db.StuCourse, s => s.Sno, stu => stu.Sno, (s, stu) => new { Sno=s.Sno,SCSno=stu.Sno,s.Sname,stu.Cid});
            GridView2.DataSource = stu5;
            GridView2.DataBind();

            //左连接
            var leftJoin = from stu in db.Student
                           join sc in db.StuCourse
                           on stu.Sno equals sc.Sno
                           into temp
                           from t in temp.DefaultIfEmpty()
                           select new { stu.Sno, stu.Sage, Cid = t == null ? 0 : t.Cid };

            //右连接
            var right = from sc in db.StuCourse
                        join stu in db.Student
                        on sc.Sno equals stu.Sno
                        into temp
                        from tt in temp.DefaultIfEmpty()
                        select new { sc.Cid, sc.Sno, SName = tt == null ? "" : tt.Sname };

            //5、标准运算符之分组——GroupBy
             //按照年龄分组
            var stu6 = db.Student.GroupBy<Student, int>(s => (int)s.Sage);
            List<IGrouping<int, Student>> list2 = stu6.ToList();
            foreach (IGrouping<int,Student> item in list2)
            {
                //输出 小组 的 分组条件
                Response.Write(string.Format("小组：{0}<br/>",item.Key));
                //遍历 小组里 所有的 元素
                foreach (Student st in item)
                {
                    Response.Write(string.Format("姓名：{0}", st.Sname));
                }
                Response.Write("<br/>");
            }

            //6、标准运算符之分页数据——Skip + Take
            //假设每页有5条记录
            //  int pageSize = 2;
            //return list.Skip((pageIndex - 1) * pageSize).Take(pageSize).ToList();
            var pageOne = db.Student.Skip<Student>(24).Take(6);
            GridView1.DataSource = pageOne;
            GridView1.DataBind();       

            #endregion

附加：

            int[] numbers = { 0, 30, 15, 90, 85, 40, 75,20, };
            int[] arr = { };
            int first = numbers.First<int>(m => m > 35); // 返回满足条件的第一条记录 90
            int last = numbers.Last<int>(n => n < 40);  //返回满足条件的最后一条记录 20
            bool allResult = numbers.All<int>(mm => mm < 100); //判断所有元素是否都满足  true
            bool allResult2 = numbers.All<int>(mm => mm>5); // false
            bool anyResult = numbers.Any(); //numbers中有元素 就返回 true
            bool anyResult1 = arr.Any();    //arr中没有元素 返回false
            bool anyResult2 = numbers.Any<int>(mm => mm <1);  // 只要有一个元素满足条件 就返回true
            bool anyResult3 = numbers.Any<int>(mm => mm >89); //true
            bool anyResult5 = numbers.Any(m => m > 200); //false