Mybatis多对一，一对多

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• • 1.多对一
  • 2.一对多

一对多：集合，一个老师有多个学生

多对一：关联association，多个学生关联一个老师

student表

teacher表

sql语句查询学生和关联的老师

select sid, sname,tname from mybatis_study.student s,mybatis_study.teacher t where s.tid=t.tid

pojo层

@Data
public class Student {
    private int sid;
    private String sname;
    private Teacher teacher;
}

@Data
public class Teacher {
    private int tid;
    private String tname;
}

mybatis-config.xml

StudentMapper.java接口

List getStudent();
List getStudent2();

映射配置StudentMapper.xml

• 按照查询嵌套处理

  
  
    select * from student
  
  
    select * from teacher where tid = #{tid}
  
  
   
   
   
  

 
按照结果嵌套处理
 
 
 
    select s.sid,s.sname,t.tname from student s,teacher,t where s.tid = t.tid;
 
 
   
   
   
     
   
 

测试类

@Test
public void getStudent2(){
    SqlSession session = MybatisUtil.getSqlSession();
    StudentMapper mapper = session.getMapper(StudentMapper.class);
    List student = mapper.getStudent();
    for (Student student1 : student) {
        System.out.println(student1);
    }
    session.close();
}