Mybatis使用@one和@Many实现一对一及一对多关联查询
目录
- 一、准备工作
- 1.创建springboot项目,项目结构如下
- 2.添加pom.xml配置信息
- 3.配置相关信息
- 二、使用@One注解实现一对一关联查询
- 三、使用@Many注解实现一对多关联查询
- 四、FetchType.LAZY 和 FetchType.EAGER的区别
一、准备工作
1.创建springboot项目,项目结构如下
2.添加pom.xml配置信息
<dependencies> <dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis</artifactId> <version>3.4.2</version> </dependency> <dependency> <groupId>org.mybatis.spring.boot</groupId> <artifactId>mybatis-spring-boot-starter</artifactId> <version>1.3.0</version> </dependency> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>5.1.34</version> </dependency> </dependencies>
3.配置相关信息
将默认的application.properties文件的后缀修改为“.yml”,即配置文件名称为:application.yml,并配置以下信息:
spring: #DataSource数据源 datasource: url: jdbc:mysql://localhost:3306/mybatis_test?useSSL=false& username: root password: root driver-class-name: com.mysql.jdbc.Driver #MyBatis配置 mybatis: type-aliases-package: com.mye.hl07mybatis.api.pojo #别名定义 configuration: log-impl: org.apache.ibatis.logging.stdout.StdOutImpl #指定 MyBatis 所用日志的具体实现,未指定时将自动查找 map-underscore-to-camel-case: true #开启自动驼峰命名规则(camel case)映射 lazy-loading-enabled: true #开启延时加载开关 aggressive-lazy-loading: false #将积极加载改为消极加载(即按需加载),默认值就是false lazy-load-trigger-methods: "" #阻挡不相干的操作触发,实现懒加载 cache-enabled: true #打开全局缓存开关(二级环境),默认值就是true
二、使用@One注解实现一对一关联查询
需求:获取用户信息,同时获取一对多关联的权限列表
1.在MySQL数据库中创建用户信息表(tb_user)
-- 判断数据表是否存在,存在则删除 DROP TABLE IF EXISTS tb_user; -- 创建“用户信息”数据表 CREATE TABLE IF NOT EXISTS tb_user ( user_id INT AUTO_INCREMENT PRIMARY KEY COMMENT '用户编号', user_account VARCHAR(50) NOT NULL COMMENT '用户账号', user_password VARCHAR(50) NOT NULL COMMENT '用户密码', blog_url VARCHAR(50) NOT NULL COMMENT '博客地址', remark VARCHAR(50) COMMENT '备注' ) COMMENT = '用户信息表'; -- 添加数据 INSERT INTO tb_user(user_account,user_password,blog_url,remark) VALUES('拒绝熬夜啊的博客','123456','https://blog.csdn.net/weixin_43296313/','您好,欢迎访问拒绝熬夜啊的博客');
2.在MySQL数据库中创建身份证信息表(tb_idcard)
-- 判断数据表是否存在,存在则删除 DROP TABLE IF EXISTS tb_idcard; -- 创建“身份证信息”数据表 CREATE TABLE IF NOT EXISTS tb_idcard ( id INT AUTO_INCREMENT PRIMARY KEY COMMENT '身份证ID', user_id INT NOT NULL COMMENT '用户编号', idCard_code VARCHAR(45) COMMENT '身份证号码' ) COMMENT = '身份证信息表'; -- 添加数据 INSERT INTO tb_idcard(user_id,idCard_code) VALUE(1,'123456789');
3.创建用户信息持久化类(UserInfo.java)
@Data @AllArgsConstructor @NoArgsConstructor public class UserInfo { private int userId; //用户编号 private String userAccount; //用户账号 private String userPassword; //用户密码 private String blogUrl; //博客地址 private String remark; //备注 private IdcardInfo idcardInfo; //身份证信息 }
4.创建身份证信息持久化类(IdcardInfo.java)
@Data @AllArgsConstructor @NoArgsConstructor public class IdcardInfo { public int id; //身份证ID public int userId; //用户编号 public String idCardCode; //身份证号码 }
5.创建UserMapper接口(用户信息Mapper动态代理接口)
@Repository @Mapper public interface UserMapper { /** * 获取用户信息和身份证信息 * 一对一关联查询 */ @Select("SELECT * FROM tb_user WHERE user_id = #{userId}") @Results(id = "userAndIdcardResultMap", value = { @Result(property = "userId", column = "user_id", javaType = Integer.class, jdbcType = JdbcType.INTEGER, id = true), @Result(property = "userAccount", column = "user_account",javaType = String.class, jdbcType = JdbcType.VARCHAR), @Result(property = "userPassword", column = "user_password",javaType = String.class, jdbcType = JdbcType.VARCHAR), @Result(property = "blogUrl", column = "blog_url",javaType = String.class, jdbcType = JdbcType.VARCHAR), @Result(property = "remark", column = "remark",javaType = String.class, jdbcType = JdbcType.VARCHAR), @Result(property = "idcardInfo",column = "user_id", one = @One(select = "com.mye.hl07mybatis.api.mapper.UserMapper.getIdcardInfo", fetchType = FetchType.LAZY)) }) UserInfo getUserAndIdcardInfo(@Param("userId")int userId); /** * 根据用户ID,获取身份证信息 */ @Select("SELECT * FROM tb_idcard WHERE user_id = #{userId}") @Results(id = "idcardInfoResultMap", value = { @Result(property = "id", column = "id"), @Result(property = "userId", column = "user_id"), @Result(property = "idCardCode", column = "idCard_code")}) IdcardInfo getIdcardInfo(@Param("userId")int userId); }
6.实现实体类和数据表的映射关系
在SpringBoot启动类中加 @MapperScan(basePackages = “com.mye.hl07mybatis.api.mapper”) 注解。
@SpringBootApplication @MapperScan(basePackages = "com.mye.hl07mybatis.api.mapper") public class Hl07MybatisApplication { public static void main(String[] args) { SpringApplication.run(Hl07MybatisApplication.class, args); } }
7.编写执行方法,获取用户信息和身份证信息(一对一关联查询)
@SpringBootTest(classes = Hl07MybatisApplication.class) @RunWith(SpringRunner.class) public class Hl07MybatisApplicationTests { @Autowired private UserMapper userMapper; /** * 获取用户信息和身份证信息 * 一对一关联查询 * @author pan_junbiao */ @Test public void getUserAndIdcardInfo() { //执行Mapper代理对象的查询方法 UserInfo userInfo = userMapper.getUserAndIdcardInfo(1); //打印结果 if(userInfo!=null) { System.out.println("用户编号:" + userInfo.getUserId()); System.out.println("用户账号:" + userInfo.getUserAccount()); System.out.println("用户密码:" + userInfo.getUserPassword()); System.out.println("博客地址:" + userInfo.getBlogUrl()); System.out.println("备注信息:" + userInfo.getRemark()); System.out.println("-----------------------------------------"); //获取身份证信息 IdcardInfo idcardInfo = userInfo.getIdcardInfo(); if(idcardInfo!=null) { System.out.println("身份证ID:" + idcardInfo.getId()); System.out.println("用户编号:" + idcardInfo.getUserId()); System.out.println("身份证号码:" + idcardInfo.getIdCardCode()); } } } }
执行结果:
三、使用@Many注解实现一对多关联查询
需求:获取用户信息,同时获取一对多关联的权限列表
1.在MySQL数据库创建权限信息表(tb_role)
-- 判断数据表是否存在,存在则删除 DROP TABLE IF EXISTS tb_role; -- 创建“权限信息”数据表 CREATE TABLE IF NOT EXISTS tb_role ( id INT AUTO_INCREMENT PRIMARY KEY COMMENT '权限ID', user_id INT NOT NULL COMMENT '用户编号', role_name VARCHAR(50) NOT NULL COMMENT '权限名称' ) COMMENT = '权限信息表'; INSERT INTO tb_role(user_id,role_name) VALUES(1,'系统管理员'),(1,'新闻管理员'),(1,'广告管理员');
2.创建权限信息持久化类(RoleInfo.java)
@Data @AllArgsConstructor @NoArgsConstructor public class RoleInfo { private int id; //权限ID private int userId; //用户编号 private String roleName; //权限名称 }
3.修改用户信息持久化类(UserInfo.java),添加权限列表的属性字段
@Data @AllArgsConstructor @NoArgsConstructor public class UserInfo { private int userId; //用户编号 private String userAccount; //用户账号 private String userPassword; //用户密码 private String blogUrl; //博客地址 private String remark; //备注 private IdcardInfo idcardInfo; //身份证信息 private List<RoleInfo> roleInfoList; //权限列表 }
4.编写用户信息Mapper动态代理接口(UserMapper.java)
/** * 获取用户信息和权限列表 * 一对多关联查询 * @author pan_junbiao */ @Select("SELECT * FROM tb_user WHERE user_id = #{userId}") @Results(id = "userAndRolesResultMap", value = { @Result(property = "userId", column = "user_id", javaType = Integer.class, jdbcType = JdbcType.INTEGER, id = true), @Result(property = "userAccount", column = "user_account",javaType = String.class, jdbcType = JdbcType.VARCHAR), @Result(property = "userPassword", column = "user_password",javaType = String.class, jdbcType = JdbcType.VARCHAR), @Result(property = "blogUrl", column = "blog_url",javaType = String.class, jdbcType = JdbcType.VARCHAR), @Result(property = "remark", column = "remark",javaType = String.class, jdbcType = JdbcType.VARCHAR), @Result(property = "roleInfoList",column = "user_id", many = @Many(select = "com.pjb.mapper.UserMapper.getRoleList", fetchType = FetchType.LAZY)) }) public UserInfo getUserAndRolesInfo(@Param("userId")int userId); /** * 根据用户ID,获取权限列表 * @author pan_junbiao */ @Select("SELECT * FROM tb_role WHERE user_id = #{userId}") @Results(id = "roleInfoResultMap", value = { @Result(property = "id", column = "id"), @Result(property = "userId", column = "user_id"), @Result(property = "roleName", column = "role_name")}) public List<RoleInfo> getRoleList(@Param("userId")int userId);
5.编写执行方法,获取用户信息和权限列表(一对多关联查询)
/** * 获取用户信息和权限列表 * 一对多关联查询 * @author pan_junbiao */ @Test public void getUserAndRolesInfo() { //执行Mapper代理对象的查询方法 UserInfo userInfo = userMapper.getUserAndRolesInfo(1); //打印结果 if(userInfo!=null) { System.out.println("用户编号:" + userInfo.getUserId()); System.out.println("用户账号:" + userInfo.getUserAccount()); System.out.println("用户密码:" + userInfo.getUserPassword()); System.out.println("博客地址:" + userInfo.getBlogUrl()); System.out.println("备注信息:" + userInfo.getRemark()); System.out.println("-----------------------------------------"); //获取权限列表 List<RoleInfo> roleInfoList = userInfo.getRoleInfoList(); if(roleInfoList!=null && roleInfoList.size()>0) { System.out.println("用户拥有的权限:"); for (RoleInfo roleInfo : roleInfoList) { System.out.println(roleInfo.getRoleName()); } } } }
执行结果:
四、FetchType.LAZY 和 FetchType.EAGER的区别
FetchType.LAZY:懒加载,加载一个实体时,定义懒加载的属性不会马上从数据库中加载。
FetchType.EAGER:急加载,加载一个实体时,定义急加载的属性会立即从数据库中加载。
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