mybatis-plus selectPage与一对多、多对多查询

mybatis-plus selectPage与一对多查询时存在问题。
1.1实体类

@Data
@NoArgsConstructor
@AllArgsConstructor
@TableName("sys_class")
public class ClassInfo {

    @TableId(type = IdType.AUTO)
    private Integer id;
    private String grade;
    private String className;
    private String classNickname;
    private String ratedNum;

    @TableField(fill = FieldFill.INSERT)
    @JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss",timezone = "GMT+8")
    private Date createTime;  //创建时间

    @TableField(fill = FieldFill.UPDATE)
    @JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss",timezone = "GMT+8")
    private Date updateTime;  //更新时间

    @TableField(exist = false) // 属性字段在表中不存在
    private List studentList;      //该班级的学生
    @TableField(exist = false) // 属性字段在表中不存在
    private List teacherList;      //管理该班级的教师
}

@Data
@NoArgsConstructor
@AllArgsConstructor
@TableName("sys_student")
public class Student {

    @TableId(type = IdType.AUTO)
    private Integer id;
    private String name;
    private String username;
    private String password;
    private SexEnum sex;
    private Date birth;
    private Date schoolDate;
    private Integer classId;
    private String portrait; //头像

    @TableField(fill = FieldFill.INSERT)
    @JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss", timezone = "GMT+8")
    private Date createTime;  //创建时间

    @TableField(fill = FieldFill.UPDATE)
    @JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss", timezone = "GMT+8")
    private Date updateTime;  //更新时间

    @TableField(exist = false)// 属性字段在表中不存在
    private ClassInfo classInfo;//当前学生的班级
    @TableField(exist = false) // 属性字段在表中不存在
    private List familyList;  //当前学生的家长
}

1.2ClassInfoMapper.java

public interface ClassInfoMapper extends baseMapper {
    //    一对多查询
    Page findPage(Page page, @Param("className") String className);

    //所有班级id
    @Select("select id  from sys_class")
    List getClassIds();
}

1.3原mapper.xml如下：

  
   --         as别名与column一致,column与mysql表字段一致，property与java实体一致
         
         
         
         
         
         
         
         
             
             
             
         
     
     
         select c.*, s.id as s_id,s.name s_name,s.sex s_sex
         from sys_class c left join sys_student s
         on c.id =s.class_id
         where c.class_name like concat('%',#{className},'%')
     
 
1.4原查询结果：
 
2.解决方案： 
分两次sql查询：
 
 
        
        
        
        
        
        
        
        
            
            
            
        
    
    
    
--         as别名与column一致,column与mysql表字段一致，property与java实体一致
         select c.*
         from sys_class c
         where c.class_name like concat('%',#{className},'%')
    
    
    
        select s.id,s.name,s.sex
        from sys_student s
        where s.class_id=#{id}
    
 
附：多对多查询
 表结构：sys_student，sys_family，中间表sys_student_family
 
    
    
        
        
        
        
        
            
            
            
            
        
    
    
    
         select s.id,s.name,s.sex,s.portrait
         from sys_student s
         where s.name like concat('%',#{name},'%')
    
    
    
        select f.id,f.name,f.sex,f.portrait
        from sys_family f join sys_student_family sf
        where f.id = sf.family_id
		and #{id} = sf.student_id
    

查询结果：