Mybatis多对一查询

Mybatis多对一查询

复杂方法

两个实体类

Student

@Data
@NoArgsConstructor
@AllArgsConstructor
public class Student {
    private int id;
    private String name;
    private Teacher teacher;
}

Teacher

@Data
@NoArgsConstructor
@AllArgsConstructor
public class Teacher {
   private int id;
   private String name;

}

@Data @NoArgsConstructor @AllArgsConstructor这三个注解为了生成构造方法和get、set

两个表

StudentMapper.java接口

List queryStudent();

Teacher getTeacher(@Param("id")int id);

StudentMapper.xml

    
    
    



    select * from student
做Student的查询


    select * from teacher where id=#{id}
做teacher的查询根据id因为数据库表里是int tid

测试类

 @Test
  public void stuter(){
      SqlSession session = MybatisUtils.getsqlsession();
     StudentMapper studentMapper = session.getMapper(StudentMapper.class);
      List students = studentMapper.queryStudent();
      for (Student student : students) {
          System.out.println(student);
      }
      session.close();
  }

简单点方法

表、实体类相同

接口只需要

List queryStudent();

Mapper.xml

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



    
    
    
        
    

测试类相同