mybatis中的result的bigint转long是null

的问题该怎么解决？

该问题可能是由于result中的bigint值为空导致的。您可以在MyBatis的映射文件中使用COALESCE函数来处理该问题，将空值转换为0或其他默认值。例如：

<result column="id" property="id" jdbcType="BIGINT" select="COALESCE(id, 0)"/>

这样可以确保即使bigint值为空，MyBatis也可以正确地将其转换为long类型。

相关问题

假设我们已经有了以下两张表： 一级菜单表 first_menu： 字段名 类型 描述 id bigint 主键 name varchar 菜单名称 url varchar 菜单链接 二级菜单表 second_menu： 字段名 类型 描述 id bigint 主键 name varchar 菜单名称 url varchar 菜单链接 first_menu_id bigint 所属的一级菜单id 现在我们需要创建一张标记是否被选中的用户-菜单表 user_menu： 字段名 类型 描述 id bigint 主键 user_id bigint 用户id menu_id bigint 菜单id selected boolean 是否被选中 java 详细设计，使用mybatis 操作数据库

首先，我们需要建立三个实体类，分别对应三张表：

FirstMenu.java

public class FirstMenu {
    private Long id;
    private String name;
    private String url;
    
    // 省略getter和setter
}

SecondMenu.java

public class SecondMenu {
    private Long id;
    private String name;
    private String url;
    private Long firstMenuId;
    
    // 省略getter和setter
}

UserMenu.java

public class UserMenu {
    private Long id;
    private Long userId;
    private Long menuId;
    private boolean selected;
    
    // 省略getter和setter
}

然后，我们需要创建对应的Mapper接口和XML文件：

FirstMenuMapper.java

public interface FirstMenuMapper {
    List<FirstMenu> findAll();
}

FirstMenuMapper.xml

<mapper namespace="com.example.mapper.FirstMenuMapper">
    <resultMap id="firstMenuMap" type="com.example.entity.FirstMenu">
        <id column="id" property="id"/>
        <result column="name" property="name"/>
        <result column="url" property="url"/>
    </resultMap>

    <select id="findAll" resultMap="firstMenuMap">
        select id, name, url from first_menu;
    </select>
</mapper>

SecondMenuMapper.java

public interface SecondMenuMapper {
    List<SecondMenu> findByFirstMenuId(Long firstMenuId);
}

SecondMenuMapper.xml

<mapper namespace="com.example.mapper.SecondMenuMapper">
    <resultMap id="secondMenuMap" type="com.example.entity.SecondMenu">
        <id column="id" property="id"/>
        <result column="name" property="name"/>
        <result column="url" property="url"/>
        <result column="first_menu_id" property="firstMenuId"/>
    </resultMap>

    <select id="findByFirstMenuId" parameterType="Long" resultMap="secondMenuMap">
        select id, name, url, first_menu_id from second_menu where first_menu_id = #{firstMenuId};
    </select>
</mapper>

UserMenuMapper.java

public interface UserMenuMapper {
    void save(UserMenu userMenu);
    UserMenu findByUserIdAndMenuId(Long userId, Long menuId);
    void updateSelected(Long id, boolean selected);
}

UserMenuMapper.xml

<mapper namespace="com.example.mapper.UserMenuMapper">
    <insert id="save" parameterType="com.example.entity.UserMenu">
        insert into user_menu (user_id, menu_id, selected) values (#{userId}, #{menuId}, #{selected});
    </insert>

    <resultMap id="userMenuMap" type="com.example.entity.UserMenu">
        <id column="id" property="id"/>
        <result column="user_id" property="userId"/>
        <result column="menu_id" property="menuId"/>
        <result column="selected" property="selected"/>
    </resultMap>

    <select id="findByUserIdAndMenuId" parameterType="map" resultMap="userMenuMap">
        select * from user_menu where user_id = #{userId} and menu_id = #{menuId};
    </select>

    <update id="updateSelected" parameterType="map">
        update user_menu set selected = #{selected} where id = #{id};
    </update>
</mapper>

最后，我们在Service层进行对应的逻辑操作：

MenuService.java

@Service
public class MenuService {
    @Autowired
    private FirstMenuMapper firstMenuMapper;

    @Autowired
    private SecondMenuMapper secondMenuMapper;

    @Autowired
    private UserMenuMapper userMenuMapper;

    public List<FirstMenu> findAllFirstMenu() {
        return firstMenuMapper.findAll();
    }

    public List<SecondMenu> findByFirstMenuId(Long firstMenuId) {
        return secondMenuMapper.findByFirstMenuId(firstMenuId);
    }

    public void saveUserMenu(Long userId, Long menuId) {
        UserMenu userMenu = userMenuMapper.findByUserIdAndMenuId(userId, menuId);
        if (userMenu == null) {
            userMenu = new UserMenu();
            userMenu.setUserId(userId);
            userMenu.setMenuId(menuId);
            userMenu.setSelected(true);
            userMenuMapper.save(userMenu);
        } else {
            userMenuMapper.updateSelected(userMenu.getId(), !userMenu.isSelected());
        }
    }
}

这样，我们就完成了对应的需求。其中，第一个方法用于获取所有一级菜单；第二个方法用于根据一级菜单id获取对应的二级菜单；第三个方法用于保存或更新用户-菜单表中的选中状态。

create table cic_bracket ( id bigint auto_increment primary key, bracket_no varchar(6) not null comment '胶托编号', owning_airport char(3) not null comment '所属站点', current_airport varchar(3) null comment '当前站点', bluetooth_id bigint null comment '蓝牙id', bluetooth_mac varchar(12) null comment '蓝牙MAC地址', create_time timestamp default CURRENT_TIMESTAMP not null comment '创建时间', update_time datetime default CURRENT_TIMESTAMP not null on update CURRENT_TIMESTAMP comment '更新时间' ) comment '胶托信息';。基于该表，使用spring，springboot，MybatisPlus框架生成增删改查功能代码

好的，以下是生成增删改查功能代码的步骤：

1. 首先，在pom.xml文件中添加以下依赖：

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>    
<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus-boot-starter</artifactId>
    <version>3.4.0</version>
</dependency>    
<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>druid-spring-boot-starter</artifactId>
    <version>1.2.6</version>
</dependency>

2. 在application.properties文件中添加以下配置：

# 数据源配置
spring.datasource.url=jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=utf-8&useSSL=false&serverTimezone=Asia/Shanghai
spring.datasource.username=root
spring.datasource.password=root
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver

# MybatisPlus配置
mybatis-plus.mapper-locations=classpath:mapper/**/*.xml
mybatis-plus.type-aliases-package=com.example.demo.entity

# Druid监控配置
spring.datasource.druid.stat-view-servlet.login-username=admin
spring.datasource.druid.stat-view-servlet.login-password=admin
spring.datasource.druid.stat-view-servlet.allow=127.0.0.1
spring.datasource.druid.stat-view-servlet.deny=

3. 创建实体类CicBracket.java：

@Data
@TableName("cic_bracket")
public class CicBracket {
    @TableId(type = IdType.AUTO)
    private Long id;

    @NotBlank(message = "胶托编号不能为空")
    private String bracketNo;

    @NotBlank(message = "所属站点不能为空")
    @Length(min = 3, max = 3, message = "所属站点必须为3位字符")
    private String owningAirport;

    private String currentAirport;

    private Long bluetoothId;

    private String bluetoothMac;

    @TableField(fill = FieldFill.INSERT)
    private Date createTime;

    @TableField(fill = FieldFill.INSERT_UPDATE)
    private Date updateTime;
}

4. 创建mapper接口CicBracketMapper.java：

@Mapper
public interface CicBracketMapper extends BaseMapper<CicBracket> {
}

5. 创建service接口ICicBracketService.java：

public interface ICicBracketService extends IService<CicBracket> {
}

6. 创建service实现类CicBracketServiceImpl.java：

@Service
public class CicBracketServiceImpl extends ServiceImpl<CicBracketMapper, CicBracket> implements ICicBracketService {
}

7. 创建controller类CicBracketController.java：

@RestController
@RequestMapping("/cic-bracket")
public class CicBracketController {
    @Autowired
    private ICicBracketService cicBracketService;

    @PostMapping("/add")
    public Result add(@Validated @RequestBody CicBracket cicBracket) {
        cicBracketService.save(cicBracket);
        return Result.ok();
    }

    @PostMapping("/update")
    public Result update(@Validated @RequestBody CicBracket cicBracket) {
        cicBracketService.updateById(cicBracket);
        return Result.ok();
    }

    @GetMapping("/delete/{id}")
    public Result delete(@PathVariable Long id) {
        cicBracketService.removeById(id);
        return Result.ok();
    }

    @GetMapping("/get/{id}")
    public Result get(@PathVariable Long id) {
        CicBracket cicBracket = cicBracketService.getById(id);
        return Result.ok().put("data", cicBracket);
    }

    @GetMapping("/list")
    public Result list() {
        List<CicBracket> list = cicBracketService.list();
        return Result.ok().put("data", list);
    }
}

8. 最后，启动Spring Boot项目，访问http://localhost:8080/swagger-ui.html，即可使用Swagger测试接口。

以上就是基于该表，使用Spring Boot、MybatisPlus框架生成增删改查功能代码的步骤，如果有疑问可以随时问我。