LINQ----1

Student[] stAry ={
                              new Student("张三","男",18),
                              new Student("小明","男",18),
                              new Student("丽丽","女",18),
                              new Student("小菊","女",18),
                              new Student("张四","男",18),
                              new Student("张八","男",18),
                          };
            var query1 = from vall in stAry
                         select vall;
            foreach (Student st in query1)
                System.Console.WriteLine(st);
            var query2 = from val2 in stAry select val2.Age;
            foreach (var age in query2)
            {
                System.Console.WriteLine("{0}",age);
            }
            var query3 = from val2 in stAry select val2.Name.Length ;
            foreach (var name in query3)
            {
                System.Console.WriteLine(name);
            }

 

where 的用法：

int[] ary = { 1, 3, 9, 12, 34, 12, 25, 33, 67, 45, 78 };
            var query1 = from val1 in ary where val1 > 15 select val1;
            foreach (var val in query1)
                System.Console.WriteLine(val);

 

orderby的用法：

Student [] stary=
            {
                 new Student ("王小二","男",17),
                 new Student ("张武率军","男",22),
                  new Student ("徐暾于灏","男",22),
                  new Student ("一朵鲜花","女",18),
            };
            var query1 = from val1 in stary
                         orderby val1.Age
                         select val1;
            foreach (var st in query1)
            {
                System.Console.WriteLine("{0}--{1}--{2}", st.Name, st.XingBie, st.Age);
            }

默认为升序，ascending，可以设置为降序 desending。

可以指定多个关键字

如果同一个查询中出现多个orderby，则只有最后一个有效。与where的取并集的效果不同。

 

 

 

用group 分组：

var query1 = from st in stary
                         group st by st.XingBie;
            foreach (var grp in query1)
            {
                System.Console.WriteLine(grp.Key);
                foreach(var stu in grp)
                {
                    System.Console.WriteLine(stu);
                }
            }
            var query2 = from st in stary
                         group st by st.Age into stgrp_age
                         select stgrp_age;
            foreach(var age in query2)
            {
                System.Console.WriteLine(age.Key + ":");
                foreach(var stu in age)
                {
                    System.Console.WriteLine(stu);
                }
            }