Update unit test

Src/Asp.Net/SqlServerTest/UnitTest/UCustom012.cs

@@ -36,10 +36,14 @@ namespace OrmTest
             db.Insertable(new StudentA() { StudentId = 3, SchoolId = 2, Name = "清华jack" }).ExecuteCommand();
             db.Insertable(new StudentA() { StudentId = 4, SchoolId = 2, Name = "清华tom" }).ExecuteCommand();
 
+            //先用Mapper导航映射查出第二层
             var list = db.Queryable<StudentA>().Mapper(x => x.SchoolA, x => x.SchoolId).ToList();
 
+            //参数1 ：将第二层对象合并成一个集合  参数2：委托
+            //说明：如果2级对象是集合用SelectMany
             db.ThenMapper(list.Select(it => it.SchoolA), sch =>
             {
+                //参数1: room表关联字段  参数2: school表关联字段，  参数3: school当前记录
                 sch.RoomList = db.Queryable<RoomA>().SetContext(room => room.SchoolId, () => sch.SchoolId, sch).ToList();
             });