one to one - association ; //单对一，使用association one to many -

collection ; //单对多，使用collection

Nested results - column is not necessary ，javaType is necessary ！

//使用嵌套结果，column 不是必需的，但是JavaType是必需的；

nested queries - column is necessary ，javaType is not necessary ！

//使用嵌套查询，column是必需的，JavaType不是必须的，子查询自定义resultType即可！！

1. 表结构：

   t_student 表拥有属性 class_id 对应 t_class表 t_id

【1】更改Classes，添加属性

public class Classes {    private int id;    private String name;    private Teacher teacher;    private List
    
      list;    ...}
    

【2】嵌套结果-获取Classes，Teacher AND list

        select * from t_class c,t_student s ,t_teacher where c.c_id = s.class_id and c.t_id = t_teacher.t_id and c.c_id = #{id}          
            
             
             
             
                 
                  
              
             
             
                 
                  
              
          
    

【3】嵌套查询–获取Classes，Teacher AND list

        select * from t_class c where c.c_id = #{id}                 select t_id id,t_name name from t_teacher where t_id = #{id}                     select s_id id,s_name name from t_student t where t.class_id = #{id}          
            
             
             
             
             
             
             
             
             
          
    

【4】Test

1. 获取SqlSessionFactory的工具类：

public static SqlSessionFactory getFactory(){            /* flow the src dir*/            String resource = "mybatis.xml";            /*MybatisUtils.class.getResourceAsStream(resource)----- it's wrong !!!!             * please distinguish the two up and down              * */            InputStream inputStream = MybatisUtils.class.getClassLoader().getResourceAsStream(resource);                SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(inputStream);                    return factory;        }

1. 测试方法

   @Test   public void testSelect4(){       /*set auto commit ,which equals to the above*/       SqlSession session = MybatisUtils.getFactory().openSession(true);       String statement = "com.web.mapper.classMapper.getClass4";       /*return the effect rows*/       Classes classes = session.selectOne(statement, 1);       Teacher teacher = classes.getTeacher();       List
         
           list = classes.getList();       System.out.println("result.."+classes+','+classes.getClass());       System.out.println(teacher);       System.out.println(list);   }
         

result as follows :

> result..Classes [id=1, list=[Student [id=1, name=stu1], Student [id=2,> name=stu2], Student [id=3, name=stu3]], name=计算机, teacher=Teacher> [id=1, name=李明]],class com.web.model.Classes Teacher [id=1, name=李明]> [Student [id=1, name=stu1], Student [id=2, name=stu2], Student [id=3,> name=stu3]]