Mybatis学习笔记-一对多关联
来源:互联网 发布:sql查询分析器下载 编辑:程序博客网 时间:2024/05/18 01:04
需求:根据classId查询对应的班级信息,包括学生,老师
Student实体类
public class Student { private int id; private String name; //...}
Classes 实体类
public class Classes { private int id; private String name; private Teacher teacher; private List<Student> students; //...}
Student实体类
public class Student {private int id;private String name;//...}
方式一: 嵌套结果: 使用嵌套结果映射来处理重复的联合结果的子集
select * from class c, teacher t,student s where c.teacher_id=t.t_id and c.c_id=s.class_id and c.c_id=#{id}
<select id="getClass" parameterType="int" resultMap="ClassResultMap3">select * from class c, teacher t,student s where c.teacher_id=t.t_id and c.c_id=s.class_id and c.c_id=#{id}</select><resultMap type="com.mybatis.test04.Classes" id="ClassResultMap3"><id property="id" column="c_id"/><result property="name" column="c_name"/><association property="teacher" column="teacher_id" javaType="com.mybatis.test04.Teacher"><id property="id" column="t_id"/><result property="name" column="t_name"/></association><!-- ofType指定students集合中的对象类型 --><collection property="students" ofType="com.mybatis.test04.Student"><id property="id" column="s_id"/><result property="name" column="s_name"/></collection></resultMap>
方式二:嵌套查询:通过执行另外一个SQL映射语句来返回预期的复杂类型
SELECT * FROM class WHERE c_id=1;
SELECT * FROM teacher WHERE t_id=1 //1 是上一个查询得到的teacher_id的值
SELECT * FROM student WHERE class_id=1 //1是第一个查询得到的c_id字段的值
<select id="getClass2" resultMap="getClass2Map">select * from class where c_id=#{id}</select><select id="getTeacher" resultType="com.mybatis.test04.Teacher">select t_id id, t_name name from teacher where t_id=#{id}</select><select id="getStudent" resultType="com.mybatis.test04.Student">select s_id id, s_name name from student where class_id=#{id}</select><resultMap type="com.mybatis.test04.Classes" id="getClass2Map"><id property="id" column="c_id"/><result property="name" column="c_name"/><association property="teacher" column="teacher_id" select="getTeacher"></association><collection property="students" column="c_id" select="getStudent"></collection></resultMap>
collection 一对多关联
ofType 指定集合中元素对象的类型
附:建表语句
DROP TABLE IF EXISTS `teacher`;CREATE TABLE `teacher` ( `t_id` int(11) NOT NULL auto_increment, `t_name` varchar(20) default NULL, PRIMARY KEY (`t_id`)) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;INSERT INTO `teacher` VALUES ('1', '孔子');INSERT INTO `teacher` VALUES ('2', '孟子');DROP TABLE IF EXISTS `class`;CREATE TABLE `class` ( `c_id` int(11) NOT NULL auto_increment, `c_name` varchar(20) default NULL, `teacher_id` int(11) default NULL, PRIMARY KEY (`c_id`), KEY `fk_teacher_id` (`teacher_id`), CONSTRAINT `fk_teacher_id` FOREIGN KEY (`teacher_id`) REFERENCES `teacher` (`t_id`)) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;INSERT INTO `class` VALUES ('1', '1121班', '1');INSERT INTO `class` VALUES ('2', '1122班', '2');DROP TABLE IF EXISTS `student`;CREATE TABLE `student` ( `s_id` int(11) NOT NULL auto_increment, `s_name` varchar(20) default NULL, `class_id` int(11) default NULL, PRIMARY KEY (`s_id`)) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8;INSERT INTO `student` VALUES ('1', '张三', '1');INSERT INTO `student` VALUES ('2', '李四', '1');INSERT INTO `student` VALUES ('3', '王五', '1');INSERT INTO `student` VALUES ('4', 'Tom', '2');INSERT INTO `student` VALUES ('5', 'Jack', '2');INSERT INTO `student` VALUES ('6', 'Robert', '2');
本文出自 “优赛工作室” 博客,请务必保留此出处http://shamrock.blog.51cto.com/2079212/1559272
0 0
- Mybatis学习笔记-一对多关联
- mybatis学习笔记(五) --- 一对多关联
- mybatis学习笔记(十)一对多关联表查询
- MyBatis学习笔记:一对一和一对多关联表查询
- Mybatis学习笔记-关联表查询的问题 (一对多关联)
- Mybatis一对多关联
- mybatis一对多关联
- 【Mybatis学习笔记】系列之二:Mybatis双项一对多关联
- MyBatis一对多双向关联——MyBatis学习笔记之七
- MyBatis学习(六):MyBatis的一对多关联如何操作
- myBatis学习笔记(5)——一对多关联表查询
- mybatis---一对多双向关联
- Mybatis一对多双向关联
- Mybatis一对多关联查询
- mybatis一对多关联关系
- Mybatis 一对多关联注解
- mybatis一对多关联查询
- Mybatis一对多关联查询
- Spring4学习笔记-Spring4整合Hibernate4
- Mybatis学习笔记-入门
- Mybatis学习笔记-CURD(基于配置文件的方式)
- Mybatis学习笔记-CURD(基于注解的方式)
- Mybatis学习笔记-一对一关联
- Mybatis学习笔记-一对多关联
- Mybatis学习笔记-动态SQL与模糊查询
- Mybatis学习笔记-调用存储过程
- Mybatis学习笔记-一级缓存与二级缓存
- HDU 2509 Be the Winner (Nim博弈)
- Mybatis学习笔记-Mybatis与Spring的整合
- Ajax学习笔记-入门笔记
- Ajax学习笔记-Ajax数据格式
- Ajax学习笔记-JQuery中的Ajax