using (testEntities TestEntity = new testEntities())            {                #region linq to entities 内容练习2                #region 父子关系表查询                /*                var maxScorePerClass = from s in TestEntity.stuinfo                                       group s by s.classID into s1                                       select new                                       {                                           classid = s1.Key,                                           stuinfo = from s2 in s1                                                     where s2.score == s1.Max(p => p.score)                                                     select s2                                       };                foreach (var sc in maxScorePerClass)  //stuinfo 为 IEnumerable
    
      类型                {                    Console.WriteLine("classID:{0}", sc.classid);                    Console.WriteLine("每班最高分数：{0}", sc.stuinfo.First().score);                }                Console.WriteLine();                 */                #endregion                #region 查询每班低于平均成绩的学生                /*                var LitThanAvgScorePerClass = from s in TestEntity.stuinfo                                              group s by s.classID into s1                                              select new                                              {                                                  classid = s1.Key,                                                  stuinfo = from s2 in s1                                                            where s2.score <= s1.Average(p => p.score)//修改此处，可查每班最低成绩、最高成绩等                                                            select s2                                              };                //     Console.Clear();                foreach (var sc in LitThanAvgScorePerClass)  //stuinfo 为 IEnumerable
     
       类型                {                    Console.WriteLine("每班低于平均分数-classID:{0}", sc.classid);                    foreach (var stu in sc.stuinfo)                    {                        Console.WriteLine("分数：{0}", stu.score);                    }                }                Console.WriteLine();                 */                #endregion                #region 模糊查询---相当于like                /*                var querylike = from s in TestEntity.stuinfo                                where s.username.Contains("pkm")  //相当于like '%pkm%'                                select s;                foreach (var s in querylike)                {                    Console.WriteLine(s.username);                }                Console.WriteLine();                 */                #endregion                #region 编译查询--类似于函数                /*                var function = CompiledQuery.Compile((testEntities edm1, string user)//参数                            => from s in edm1.stuinfo                               where s.username == user                               select s                            );                var stu001 = function(TestEntity, "pkm001");//调用编译查询                foreach (var s in stu001)                {                    Console.WriteLine(s.username);                }                Console.WriteLine();                 */                #endregion                #region any查询，相当于 in                /*                IQueryable
      
        classIDs = TestEntity.classinfo.Select(c => c.classID);                var inValues = from s in TestEntity.stuinfo                               where classIDs.Any(id => id == s.classID)                               select s;                foreach (var s in inValues)                {                    Console.WriteLine(s.username);                }                Console.WriteLine();                  */                #endregion                #region 插入数据--相当于insert                /*                var newStudent = new stuinfo()                        {                            username = "test0003",                            userpwd = "test0003",                            score = 95,                            age = 30,                            classID = 2,                            CreateTime = DateTime.Now                        };                TestEntity.AddTostuinfo(newStudent);                //TestEntity.AddObject("stuinfo", newStudent);  //这句的上面一句是一样的                TestEntity.SaveChanges();                Console.Write("添加数据成功！");                 */                #endregion                #region 修改数据 -- update                /*                var toModify = (from s in TestEntity.stuinfo                                where s.id == 9                                select s).FirstOrDefault();                toModify.userpwd = "test";                TestEntity.SaveChanges(); //修改之后进行保存就行了。                  */                #endregion                #region 删除数据 delete                /*                var toDelete = (from s in TestEntity.stuinfo                                where s.id == 10                                select s).FirstOrDefault();                TestEntity.DeleteObject(toDelete);                TestEntity.SaveChanges();                  */                #endregion                #region 删除前不查询，只指定主键的值                  var deleteStu = new stuinfo                {                id = 9                };                MyEntity.AttachTo("stuinfo", deleteStu);                MyEntity.DeleteObject(deleteStu);                MyEntity.SaveChanges();//如果有此主键则删除，否则将出异常。要使用try…catch…包含                  #endregion                #region 查询结果转换为 List,Array,Dictionary                 var tempstudents = from s in TestEntity.stuinfo                                   where s.CreateTime.Value.Year == 2012                                   select s;                //stuinfo[] array = tempstudents.ToArray();                //List
       
         list = tempstudents.ToList();                Dictionary
        
          dict = tempstudents.ToDictionary(s => s.id);                foreach (var s in dict.Values)                {                    Console.WriteLine("用户：{0},密码：{1}", s.username, s.userpwd);                }                Console.WriteLine();                 #endregion                                #endregion            }