Mybatis - 表关联one-to-many

摘要：单对一，使用单对多，使用，使用嵌套结果，不是必需的，但是是必需的，使用嵌套查询，是必需的，不是必须的，子查询自定义即可表结构表拥有属性对应表更改，添加属性嵌套结果获取，嵌套查询获取，有属性有属性

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！！

表结构：

t_student 表拥有属性 class_id 对应 t_class表 t_id

public class Classes {

    private int id;
    private String name;
    private Teacher teacher;
    private List 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}
     
     
        
        

        
        
            
            
        

        
        
            
            
        
     
    
 

 
        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}
     

     
        
        

        
        
        

        
        
        
        
     
     
  

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;
        }
        

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..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]]