SpringBoot实现联表查询的代码详解

SELECT a.username,b.id FROM USER AS a LEFT JOIN ban_ji AS b ON a.ban_ji_id=b.id

 // 非数据库列 班级名字
@TableFile(exist=fale)
private String banJiName;
// 非数据库列 学院名字
@TableField(exist = false)
private String xueYuanName;
// 非数据库列 老师名字
@TableField(exist = false)
private String teacherName;

IPage<User> page=new Page<userVo.getPage(),userVo.getLimit()>
 
//创建条件构造器
QueryWrapper<User> queryWrapper=new QueryWrapper<>();
//进行模糊查询 ：根据用户名和手机号查询    queryWrapper.like(StringUtils.isNotEmpty(userVo.getUsername()),"username",userVo.getUsername());
queryWrapper.like(StringUtils.isNotEmpty(userVo.getPhone()),"phone",userVo.getPhone());
//进行查询
userService.page(page,queryWrapper);
//此时在IPage对象page中已经有了所有的数据 page.getRecords()
 
 
for(User user :page.getRecords())
{
   //判断ban_ji_name
   if(user.getBanJiId()!=null)
   {
      BanJi banji=banJiService.getById(user.getBanJiId);
      user.setBanJiName(banji.getName());
   }
   //为学院名称赋值
   if(user.getXueYuanId()!=null)
   {
      XueYuan xueyuan = xueYuanService.getById(user.getXueYuanId());
      user.setXueYuanName(xueyuan.getName());
            }
   //为老师名称赋值
   if(user.getTeacherId()!=null)
   {
      User teacher = userService.getById(user.getTeacherId());
      user.setTeacherName(teacher.getUsername());
    }
}