MyBatis-Plus 主键回填失效问题

// 错误示例
public class User {
    private Long id;  // 没有 @TableId 注解
    private String name;
}

// 正确示例
public class User {
    @TableId(type = IdType.AUTO)
    private Long id;
    private String name;
}

// 错误示例 - 数据库列名是 user_id，实体字段是 id
@TableId(type = IdType.AUTO)
private Long id;  // 数据库列名是 user_id

// 正确示例
@TableId(value = "user_id", type = IdType.AUTO)
private Long id;

// 父类
public class BaseModel {
    @TableId(type = IdType.AUTO)
    private Long id;  // 父类主键
}

// 子类 - 需要不同的主键字段
public class WarnRule extends BaseModel {
    private Long ruleId;  // 实际的主键字段
    // 其他字段...
}

public class WarnRule extends BaseModel {
    @TableId(value = "rule_id", type = IdType.AUTO)
    private Long ruleId;
    
    // 忽略父类的主键字段
    @TableField(exist = false)
    private Long id;
}

<insert id="insert" parameterType="com.example.WarnRule" 
        useGeneratedKeys="true" keyProperty="ruleId" keyColumn="rule_id">
    INSERT INTO warn_rule (dict_id, rule_name, status, create_by, create_time)
    VALUES (#{dictId}, #{ruleName}, #{status}, #{createBy}, NOW())
</insert>

// 错误示例 - 数据库主键不是自增
@TableId(type = IdType.AUTO)
private Long id;  // 但数据库表主键不是 AUTO_INCREMENT

ALTER TABLE your_table MODIFY COLUMN id BIGINT AUTO_INCREMENT PRIMARY KEY;

@TableId(type = IdType.INPUT)  // 手动输入
private Long id;

@TableId(type = IdType.ASSIGN_ID)  // 雪花算法
private Long id;

<!-- 错误示例 - 没有配置主键回填 -->
<insert id="insert" parameterType="com.example.User">
    INSERT INTO user (name, age) VALUES (#{name}, #{age})
</insert>
<!-- 正确示例 -->
<insert id="insert" parameterType="com.example.User" 
        useGeneratedKeys="true" keyProperty="id" keyColumn="id">
    INSERT INTO user (name, age) VALUES (#{name}, #{age})
</insert>

@Transactional
public void saveUser() {
    User user = new User();
    user.setName("test");
    userMapper.insert(user);
    // 如果这里抛出异常，事务回滚，user.getId() 可能为 null
    System.out.println(user.getId());  // 可能为 null
}

@Entity
@TableName("user")
public class User {
    @TableId(value = "id", type = IdType.AUTO)
    private Long id;
    
    private String name;
    private Integer age;
    
    // getter/setter...
}

// 父类 - 不定义主键
public class BaseModel {
    private String createBy;
    private Date createTime;
    private String updateBy;
    private Date updateTime;
    // 其他公共字段...
}

// 子类 - 定义自己的主键
public class WarnRule extends BaseModel {
    @TableId(value = "rule_id", type = IdType.AUTO)
    private Long ruleId;
    
    private Long dictId;
    private String ruleName;
    // 其他字段...
}

<insert id="insert" parameterType="com.example.WarnRule" 
        useGeneratedKeys="true" keyProperty="ruleId" keyColumn="rule_id">
    INSERT INTO warn_rule (
        dict_id, rule_name, status, create_by, create_time, update_by, update_time
    ) VALUES (
        #{dictId}, #{ruleName}, #{status}, #{createBy}, NOW(), #{updateBy}, NOW()
    )
</insert>

@Service
public class UserService {
    
    @Autowired
    private UserMapper userMapper;
    
    public Long saveUser(User user) {
        // 方案1：使用 MyBatis-Plus 的 insert 方法
        userMapper.insert(user);
        return user.getId();
        
        // 方案2：使用自定义方法
        // userMapper.insertWithKey(user);
        // return user.getId();
    }
}

# application.yml
mybatis-plus:
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl

@Test
public void testInsertWithKey() {
    User user = new User();
    user.setName("test");
    user.setAge(25);
    
    userMapper.insert(user);
    
    // 验证主键是否回填
    assertNotNull(user.getId());
    System.out.println("Generated ID: " + user.getId());
}