[043][数据模块]基于 Spring Data JPA 的企业级数据访问层设计——实体、审计、状态与服务抽象

public interface Entity extends Serializable { }

public interface IdEntity<ID extends Serializable> extends Entity {
    ID getId();
    void setId(ID pk);
    default boolean isNew() { return getId() == null; }
}

public interface VersionEntity extends Entity {
    Integer getVersion();
    void setVersion(Integer version);
}

public interface AuditingEntity extends Entity {
    String getCreatedBy();          // 创建人
    LocalDateTime getCreatedDate(); // 创建时间
    String getLastModifiedBy();     // 最后修改人
    LocalDateTime getLastModifiedDate();
    // 对应的 setter ...
}

public interface StatusEntity extends Entity {
    DataStatus getDataStatus();
    void setDataStatus(DataStatus status);
    
    default boolean isNormal() { return DataStatus.NORMAL.equals(getDataStatus()); }
    default boolean isDeleted() { ... }
    // 其他状态判断 ...
}

public class BaseDTO implements IdEntity<Long>, VersionEntity, AuditingEntity {
    private Long id;
    private Integer version;
    private LocalDateTime createDate = LocalDateTime.now();
    private LocalDateTime lastModifiedDate = LocalDateTime.now();
    private String createBy;
    private String lastModifiedBy;
    // 实现方法及 equals/hashCode（基于 id）
}

@MappedSuperclass
@EntityListeners(AuditingEntityListener.class)
public class BaseEntity implements IdEntity<Long>, VersionEntity, AuditingEntity {
    @Id
    @SnowflakeIdGenerator  // 自定义雪花算法主键生成器
    private Long id;
    
    @Version
    private Integer version;
    
    @Column(updatable = false)
    @CreatedDate
    private LocalDateTime createDate = LocalDateTime.now();
    
    @LastModifiedDate
    private LocalDateTime lastModifiedDate;
    
    @CreatedBy
    private String createBy;
    
    @LastModifiedBy
    private String lastModifiedBy;
    // getter/setter ...
}

@MappedSuperclass
public class BaseStatusEntity extends BaseEntity implements StatusEntity {
    @Enumerated(EnumType.STRING)
    private DataStatus status;
    
    @PrePersist
    public void prePersist() {
        if (status == null) status = DataStatus.NORMAL;
    }
    
    @PreRemove
    public void preRemove() {
        if (isReserved()) throw new RuntimeException("保留数据，不能删除");
    }
}

@NoRepositoryBean
public interface BaseRepository<E extends Entity, ID extends Serializable>
        extends JpaRepository<E, ID>, JpaSpecificationExecutor<E> {
}

default E findById(ID id) { ... }          // 不存在抛异常
default List<E> findAll(Specification<E> spec) { ... }
default Page<E> findByPage(Pageable pageable) { ... }
// 重载：排序、Example 查询、分页快捷方式等

default E save(E domain);
default void delete(E entity);
default void deleteAllInBatch();
// ... flush, saveAllAndFlush 等

@Service
public class UserService implements BaseService<User, Long> {
    @Autowired
    private UserRepository userRepository;
    
    @Override
    public BaseRepository<User, Long> getRepository() {
        return userRepository;
    }
    
    // 业务方法可直接调用继承的 findAll, save 等
    public Page<User> findNormalUsers(Pageable pageable) {
        Specification<User> spec = (root, q, cb) -> cb.equal(root.get("status"), DataStatus.NORMAL);
        return findByPage(spec, pageable);
    }
}

static <Z, X> Join<Z, X> join(Root<Z> root, String attribute, JoinType joinType) {
    // 如果已存在相同属性和类型的 join，直接返回，否则创建新的
}