Mybatis使用@one和@Many实现一对一及一对多关联查询

一、准备工作

1.创建springboot项目,项目结构如下

在这里插入图片描述

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&amp
    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:

在这里插入图片描述

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:

在这里插入图片描述

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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发布时间 2021-09-21 12:00:03
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