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目录
mybatis 复杂对象resultMap
下面是resultMap的定义
普通属性省略说明
select相关配置
Model代码
resultMap处理复杂映射问题
Ⅰ 多对一查询:学生——老师
(1) 创建实体类POJO
(2) 创建学生实体类对应的接口
(3) 编写学生接口对应的Mapper.xml
(4)在核心配置类中引入Mapper
Ⅱ 一对多查询:老师——学生
(1)实体类
(2) 接口
(3)接口对应的Mapper.xml
(4)测试:
Mybatis 复杂对象resultMap 数据对象含有普通属性,一对一对象,一对多对象(2种情况:单一主键和复合主键) 下面是resultMap的定义 普通属性省略说明 一对一属性productioncompany 一对多属性goodsnutrientList(复合主键,返回的复杂对象内有数据) 一对多属性liquorgoodsccicList(复合主键,返回的复杂对象内没有数据) 一对多属性projectgoodsList(单一主键,返回的复杂对象内有数据) select相关配置 SELECT m_goods_nutrient.* FROM m_goods_nutrient m_goods_nutrient.goods_cd = #{goods_cd} AND m_goods_nutrient.del_flg = '0' SELECT m_liquorgoods_ccic.* FROM m_liquorgoods_ccic m_liquorgoods_ccic.goods_cd = #{goods_cd} AND m_liquorgoods_ccic.del_flg = '0' SELECT t_project_goods.* FROM t_project_goods t_project_goods.goods_cd = #{goods_cd} AND t_project_goods.del_flg = '0' SELECT m_goods.*, m_production_company.*, now() AS SELECT_TIME FROM m_goods LEFT JOIN m_production_company ON m_goods.production_company_cd = m_production_company.production_company_cd AND m_production_company.del_flg = '0' WHERE m_goods.goods_cd = #{primary_key} AND m_goods.del_flg = '0' 通过findByPrimaryKey方法获取普通属性和1对1对象属性 通过getGoodsnutrient方法获取1对多复合主键的属性,注意返回类型的配置为resultMap=“GoodsnutrientResultMap”(返回的对象的List属性内有数据) 通过getLiquorgoodsccic方法获取1对多复合主键的属性,此处的返回类型为 resultType=“trade.db.model.Liquorgoodsccic”(返回的对象的List属性内没有数据) 通过getProjectgoods方法获取1对多单一主键的属性,此处的返回类型为resultType=“trade.db.model.Projectgoods”(返回的对象的List属性内有数据) Model代码 public class GoodsModelCustomize extends Goods { private Productioncompany productioncompany; public Productioncompany getProductioncompany() { return productioncompany; } public void setProductioncompany(Productioncompany productioncompany) { this.productioncompany = productioncompany; } private List goodsnutrientList; public List getGoodsnutrientList() { return goodsnutrientList; } public void setGoodsnutrientList(List goodsnutrientList) { this.goodsnutrientList = goodsnutrientList; } private List liquorgoodsccicList; public List getLiquorgoodsccicList() { return liquorgoodsccicList; } public void setLiquorgoodsccicList(List liquorgoodsccicList) { this.liquorgoodsccicList = liquorgoodsccicList; } private List projectgoodsList; public List getProjectgoodsList() { return projectgoodsList; } public void setProjectgoodsList(List projectgoodsList) { this.projectgoodsList = projectgoodsList; } } 普通属性继承与Goods代码省略,上述属性productioncompany,goodsnutrientList和projectgoodsList有数据,但是liquorgoodsccicList没有数据 因此,当返回对象内有1对多的List属性,同时此list为复合主键的话,推荐使用resultMap来对返回数据映射。 resultMap处理复杂映射问题 Ⅰ 多对一查询:学生——老师 数据库表: CREATE TABLE `teacher` ( `id` INT(10) NOT NULL, `name` VARCHAR(30) DEFAULT NULL, PRIMARY KEY (`id`) ) ENGINE=INNODB DEFAULT CHARSET=utf8; INSERT INTO teacher(`id`, `name`) VALUES (1, '王老师'); CREATE TABLE `student` ( `id` INT(10) NOT NULL, `name` VARCHAR(30) DEFAULT NULL, `tid` INT(10) DEFAULT NULL, PRIMARY KEY (`id`), KEY `fktid` (`tid`), CONSTRaiNT `fktid` FOREIGN KEY (`tid`) REFERENCES `teacher` (`id`) ) ENGINE=INNODB DEFAULT CHARSET=utf8; INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('1', '小明', '1'); INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('2', '小红', '1'); INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('3', '小张', '1'); INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('4', '小李', '1'); INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('5', '小王', '1');(1) 创建实体类POJO @Data public class Student { private int id; private String name; private Teacher teacher; } @Data public class Teacher { private int id; private String name; } (2) 创建学生实体类对应的接口 public interface StudentMapper { //查询所有学生的信息 List getStudent(); List getStudent2(); } (3) 编写学生接口对应的Mapper.xml 为了达到和接口在同一个包中的效果,在resource文件夹下新建包结构com.glp.dao:
在多对一查询中,需要用到teacher这个表,每个学生都对应着一个老师。而property只能处理单个属性,像teacher这种复杂属性(内含多个属性)需要进行处理。处理复杂对象要用association 。 方式一:联表查询(直接查出所有信息,再对结果进行处理) 直接查询出学生和老师,然后用association去取老师里面的属性property。 方式二:子查询(先查出学生信息,再拿着学生中的tid,去查询老师的信息) select * from teacher where id = #{id};在resultMap中引入属性association,通过javaType指定property="teacher"的类型,javaType="Teacher"。通过select引入子查询(嵌套查询)。 这里是拿到学生中的tid,去查找对应的老师。 (4)在核心配置类中引入Mapper db.properties:数据库连接参数配置文件 driver = com.Mysql.jdbc.Driver url=jdbc:mysql://localhost:3306/mybatis?useSSL=true&useUnicode=true&chracterEncoding=utf8 username =root passWord =mysqlmybatis.xml: 注意: 要保证接口和Mapper.xml都在同一个包中。 (5) 测试 public class UserDaoTest { @Test public void getStudent(){ SqlSession sqlSession = MyUtils.getSqlSession(); StudentMapper mapper = sqlSession.getMapper(StudentMapper.class); List list = mapper.getStudent(); for (Student stu:list ) { System.out.println(stu); } sqlSession.close(); } @Test public void getStudent2(){ SqlSession sqlSession = MyUtils.getSqlSession(); StudentMapper mapper = sqlSession.getMapper(StudentMapper.class); List list = mapper.getStudent2(); for (Student stu:list ) { System.out.println(stu); } sqlSession.close(); } }Ⅱ 一对多查询:老师——学生 (1)实体类 @Data public class Student { private int id; private String name; private int tid; } @Data public class Teacher { private int id; private String name; private List students; } (2) 接口 package com.glp.dao; public interface TeacherMapper { Teacher getTeacher(@Param("tid") int id); Teacher getTeacher2(@Param("tid") int id); } (3)接口对应的Mapper.xml select s.id sid, s.name sname, t.name tname, t.id tid from student s ,teacher t where s.tid = t.id and t.id = #{tid}; select * from teacher where id = #{tid}; select * from student where tid=#{tid}; 方式一:联表查询,需要写复杂SQL collection 用来处理集合,ofType用来指定集合中的约束类型 联合查询时,查询出所以结果,然后再解析结果中的属性,将属性property赋予到collection中。 方式二:子查询,需要写复杂映射关系 查询学生时,需要拿着老师的id去查找,column用来给出老师的id。 (4)测试: package com.glp.dao; public class UserDaoTest { @Test public void getTeacher(){ SqlSession sqlSession = MyUtils.getSqlSession(); TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class); Teacher teacher = mapper.getTeacher(1); System.out.println(teacher); sqlSession.close(); } @Test public void getTeacher2(){ SqlSession sqlSession = MyUtils.getSqlSession(); TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class); Teacher teacher = mapper.getTeacher2(1); System.out.println(teacher); sqlSession.close(); } } |
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