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一、準備工作

1.創建springboot項目，項目結構如下

Mybatis使用@one和@Many實現一對一及一對多關聯查詢

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.配置相關信息

將默認的application.properties文件的后綴修改為“.yml”，即配置文件名稱為：application.yml，并配置以下信息：

spring:
  #DataSource數據源
  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 #別名定義
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl #指定 MyBatis 所用日志的具體實現，未指定時將自動查找
    map-underscore-to-camel-case: true #開啟自動駝峰命名規則（camel case）映射
    lazy-loading-enabled: true #開啟延時加載開關
    aggressive-lazy-loading: false #將積極加載改為消極加載（即按需加載）,默認值就是false
    lazy-load-trigger-methods: "" #阻擋不相干的操作觸發，實現懶加載
    cache-enabled: true #打開全局緩存開關（二級環境），默認值就是true

二、使用@One注解實現一對一關聯查詢

需求：獲取用戶信息，同時獲取一對多關聯的權限列表

1.在MySQL數據庫中創建用戶信息表（tb_user）

-- 判斷數據表是否存在，存在則刪除
DROP TABLE IF EXISTS tb_user;
 
-- 創建“用戶信息”數據表
CREATE TABLE IF NOT EXISTS tb_user
( 
	user_id INT AUTO_INCREMENT PRIMARY KEY COMMENT "用戶編號",
	user_account VARCHAR(50) NOT NULL COMMENT "用戶賬號",
	user_password VARCHAR(50) NOT NULL COMMENT "用戶密碼",
	blog_url VARCHAR(50) NOT NULL COMMENT "博客地址",
	remark VARCHAR(50) COMMENT "備注"
) COMMENT = "用戶信息表";
 
-- 添加數據
INSERT INTO tb_user(user_account,user_password,blog_url,remark) VALUES("拒絕熬夜啊的博客","123456","https://blog.csdn.net/weixin_43296313/","您好，歡迎訪問拒絕熬夜啊的博客");

2.在MySQL數據庫中創建身份證信息表（tb_idcard）

-- 判斷數據表是否存在，存在則刪除
DROP TABLE IF EXISTS tb_idcard;
 
-- 創建“身份證信息”數據表
CREATE TABLE IF NOT EXISTS tb_idcard
( 
	id INT AUTO_INCREMENT PRIMARY KEY COMMENT "身份證ID",
	user_id INT NOT NULL COMMENT "用戶編號",
	idCard_code VARCHAR(45) COMMENT "身份證號碼"
) COMMENT = "身份證信息表";
 
-- 添加數據
INSERT INTO tb_idcard(user_id,idCard_code) VALUE(1,"123456789");

3.創建用戶信息持久化類（UserInfo.java）

@Data
@AllArgsConstructor
@NoArgsConstructor
public class UserInfo {
    private int userId; //用戶編號
    private String userAccount; //用戶賬號
    private String userPassword; //用戶密碼
    private String blogUrl; //博客地址
    private String remark; //備注
    private IdcardInfo idcardInfo; //身份證信息
}

4.創建身份證信息持久化類（IdcardInfo.java）

@Data
@AllArgsConstructor
@NoArgsConstructor
public class IdcardInfo {
    public int id; //身份證ID
    public int userId; //用戶編號
    public String idCardCode; //身份證號碼
}

5.創建UserMapper接口（用戶信息Mapper動態代理接口）

@Repository
@Mapper
public interface UserMapper {
    /**
     * 獲取用戶信息和身份證信息
     * 一對一關聯查詢
     */
    @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);
 
    /**
     * 根據用戶ID，獲取身份證信息
     */
    @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.實現實體類和數據表的映射關系

在SpringBoot啟動類中加 @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.編寫執行方法，獲取用戶信息和身份證信息（一對一關聯查詢）

@SpringBootTest(classes = Hl07MybatisApplication.class)
@RunWith(SpringRunner.class)
public class Hl07MybatisApplicationTests {

    @Autowired
    private UserMapper userMapper;

    /**
     * 獲取用戶信息和身份證信息
     * 一對一關聯查詢
     * @author pan_junbiao
     */
    @Test
    public void getUserAndIdcardInfo() {
        //執行Mapper代理對象的查詢方法
        UserInfo userInfo = userMapper.getUserAndIdcardInfo(1);
        //打印結果
        if(userInfo!=null) {
            System.out.println("用戶編號：" + userInfo.getUserId());
            System.out.println("用戶賬號：" + userInfo.getUserAccount());
            System.out.println("用戶密碼：" + userInfo.getUserPassword());
            System.out.println("博客地址：" + userInfo.getBlogUrl());
            System.out.println("備注信息：" + userInfo.getRemark());
            System.out.println("-----------------------------------------");

            //獲取身份證信息
            IdcardInfo idcardInfo = userInfo.getIdcardInfo();
            if(idcardInfo!=null) {
                System.out.println("身份證ID：" + idcardInfo.getId());
                System.out.println("用戶編號：" + idcardInfo.getUserId());
                System.out.println("身份證號碼：" + idcardInfo.getIdCardCode());
            }
        }
    }
}

執行結果：

Mybatis使用@one和@Many實現一對一及一對多關聯查詢

三、使用@Many注解實現一對多關聯查詢

需求：獲取用戶信息，同時獲取一對多關聯的權限列表

1.在MySQL數據庫創建權限信息表（tb_role）

-- 判斷數據表是否存在，存在則刪除
DROP TABLE IF EXISTS tb_role;
 
-- 創建“權限信息”數據表
CREATE TABLE IF NOT EXISTS tb_role
( 
	id INT AUTO_INCREMENT PRIMARY KEY COMMENT "權限ID",
	user_id INT NOT NULL COMMENT "用戶編號",
	role_name VARCHAR(50) NOT NULL COMMENT "權限名稱"
) COMMENT = "權限信息表";
 
INSERT INTO tb_role(user_id,role_name) VALUES(1,"系統管理員"),(1,"新聞管理員"),(1,"廣告管理員");

2.創建權限信息持久化類（RoleInfo.java）

@Data
@AllArgsConstructor
@NoArgsConstructor
public class RoleInfo {
    private int id; //權限ID
    private int userId; //用戶編號
    private String roleName; //權限名稱
}

3.修改用戶信息持久化類（UserInfo.java），添加權限列表的屬性字段

@Data
@AllArgsConstructor
@NoArgsConstructor
public class UserInfo {
    private int userId; //用戶編號
    private String userAccount; //用戶賬號
    private String userPassword; //用戶密碼
    private String blogUrl; //博客地址
    private String remark; //備注
    private IdcardInfo idcardInfo; //身份證信息
    private List<RoleInfo> roleInfoList; //權限列表
}

4.編寫用戶信息Mapper動態代理接口（UserMapper.java）

/**
 * 獲取用戶信息和權限列表
 * 一對多關聯查詢
 * @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);
 
/**
 * 根據用戶ID，獲取權限列表
 * @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.編寫執行方法，獲取用戶信息和權限列表（一對多關聯查詢）

/**
     * 獲取用戶信息和權限列表
     * 一對多關聯查詢
     * @author pan_junbiao
     */
    @Test
    public void getUserAndRolesInfo() {
        //執行Mapper代理對象的查詢方法
        UserInfo userInfo = userMapper.getUserAndRolesInfo(1);
        //打印結果
        if(userInfo!=null) {
            System.out.println("用戶編號：" + userInfo.getUserId());
            System.out.println("用戶賬號：" + userInfo.getUserAccount());
            System.out.println("用戶密碼：" + userInfo.getUserPassword());
            System.out.println("博客地址：" + userInfo.getBlogUrl());
            System.out.println("備注信息：" + userInfo.getRemark());
            System.out.println("-----------------------------------------");

            //獲取權限列表
            List<RoleInfo> roleInfoList = userInfo.getRoleInfoList();
            if(roleInfoList!=null && roleInfoList.size()>0) {
                System.out.println("用戶擁有的權限：");
                for (RoleInfo roleInfo : roleInfoList) {
                    System.out.println(roleInfo.getRoleName());
                }
            }
        }
    }