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package ad.ovo.demo2.service;
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import ad.ovo.demo2.entity.SysUser;
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public interface SysUserService {
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    SysUser getById(Long id);
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    void add(SysUser user);
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    void update(SysUser user);
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    void delete(Long id);
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}

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package ad.ovo.demo2.service.impl;
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import ad.ovo.demo2.common.exception.BizException;
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import ad.ovo.demo2.common.result.ResultCode;
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import ad.ovo.demo2.entity.SysUser;
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import ad.ovo.demo2.mapper.SysUserMapper;
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import ad.ovo.demo2.service.SysUserService;
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import lombok.RequiredArgsConstructor;
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import org.springframework.stereotype.Service;
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@Service
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@RequiredArgsConstructor
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public class SysUserServiceImpl implements SysUserService {
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    private final SysUserMapper sysUserMapper;   // 依赖注入 Mapper
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    @Override
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    public SysUser getById(Long id){
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        SysUser user = sysUserMapper.selectById(id);
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        if (user == null) {
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            throw new BizException(ResultCode.NOT_FOUND, "用户不存在: id=" + id);
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        }
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        return user;
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    }
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    @Override
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    public void add(SysUser user){
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        sysUserMapper.insert(user);
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    }
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    @Override
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    public void update(SysUser user) {
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        // 前置校验：先拦住"没带 id"的请求，再查库（防御性编程）
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        if (user == null || user.getId() == null) {
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            throw new BizException(ResultCode.NOT_FOUND, "用户信息或ID不能为空");
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        }
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        int row = sysUserMapper.updateById(user);
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        if (row == 0) {
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            throw new BizException(ResultCode.NOT_FOUND, "用户不存在：id = " + user.getId());
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        }
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    }
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    @Override
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    public void delete(Long id){
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        int row = sysUserMapper.deleteById(id);
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        if (row == 0) {
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            throw new BizException(ResultCode.NOT_FOUND, "用户不存在: id=" + id);
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        }
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    }
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}

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package ad.ovo.demo2.entity;
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import com.baomidou.mybatisplus.annotation.IdType;
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import com.baomidou.mybatisplus.annotation.TableId;
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import com.baomidou.mybatisplus.annotation.TableName;
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import jakarta.validation.constraints.NotBlank;
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import jakarta.validation.constraints.Size;
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import java.time.LocalDateTime;
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import lombok.Data;
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@Data
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@TableName("sys_user")
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public class SysUser {
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    @TableId(type = IdType.AUTO)
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    private Long id;
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    // 校验注解：新增时必须非空；groups=AddGroup 表示"仅新增场景校验"
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    @NotBlank(message = "用户名不能为空", groups = AddGroup.class)
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    private String username;
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    @Size(min = 6, max = 20, message = "密码长度必须在6-20之间", groups = AddGroup.class)
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    private String password;
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    private String nickname;
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    private Integer status;
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    private LocalDateTime createTime;
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    private LocalDateTime updateTime;
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    /** 新增场景校验分组。 */
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    public interface AddGroup {}
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    /** 更新场景校验分组：无约束，支持部分更新。 */
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    public interface UpdateGroup {}
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}

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package ad.ovo.demo2.mapper;
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import ad.ovo.demo2.entity.SysUser;
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import com.baomidou.mybatisplus.core.mapper.BaseMapper;
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import org.apache.ibatis.annotations.Mapper;
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@Mapper
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public interface SysUserMapper extends BaseMapper<SysUser> {
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}