//选课,生成一个Selection
 public bool SelectCourse(int studentId, int courseId)
 {
     //IStudentDao studentDao = new StudentDao(sessionFactory);
     ICourseDao courseDao = new CourseDao(sessionFactory);
     Course selectedCourse = courseDao.Get(courseId);
     Selection newSelection = new Selection
     {
         ID = new SelectionID {
             selectionStudentID=studentId,
             selectionCourseID=selectedCourse.courseID,
             selectionStudyYear=selectedCourse.courseStudyYear,
             selectionTerm=selectedCourse.courseTerm
         },
         selectionScorePermit=false,
         selectionScore =-1
     };
     ISelectionDao selectionDao = new SelectionDao(sessionFactory);
     if (null != selectionDao.Save(newSelection))
     {
         return true;
     }
     else {
         return false;
     }
 }
 public void Save(Selection newSelection)
 {
     ISelectionDao selectionDao = new SelectionDao(sessionFactory);
     selectionDao.Save(newSelection);
 }