一、思路1:在service封装通过list的组合，强烈不建议，有性能问题，例如：@Autowiredprivate StudentDao studentDao;@Autowiredprivate Stu_labelDao stu_labelDao;@Autowiredprivate CityDao cityDao;@Autowiredprivate ClazzDao clazzDao;@Autowiredprivate GroupDao groupDao;@Autowiredprivate LabelDao labelDao;@Testpublic void testQuesyAllStudent(){List<Student> students = studentDao.selectAll();for (Student student:students){//通用Mapper的dao方法  select（Object o），根据对象非空属性做条件查询查询//city属性List<City> cities = cityDao.select(student.getCity());City city = cities.get(0);student.setCity(city);//clazz属性List<Clazz> clazzes = clazzDao.select(student.getClazz());Clazz clazz = clazzes.get(0);student.setClazz(clazz);//group属性List<Group> groups = groupDao.select(student.getGroup());Group group = groups.get(0);student.setGroup(group);//label集合Stu_label stu_label = new Stu_label();stu_label.setSid(student.getId());List<Stu_label> stu_labels = stu_labelDao.select(stu_label);List<Label> labels = new ArrayList<>();for (Stu_label s:stu_labels){Label label = labelDao.selectByPrimaryKey(s.getLid());//主键策略，根据主键查询labels.add(label);}student.setLabels(labels);}}