用 Redis 存储 ID 连续的数据

之前在设计「Doodle 2」和开发「知乎日报」时，我面对最多的数据类型就是带 ID 的数据了。 在使用关系型数据库时，自增的主键可以满足这个需求，而在 Redis 中就稍微麻烦些了。 一直以来我都额外使用了一个计数器来存储 ID，例如（省略了很多代码，不影响阅

class IDModel(JSONModel):
    id = IntegerProperty()
    @classmethod
    def get_by_id(cls, entity_id):
        json_content = cls.redis_client.hget(cls._KEY, entity_id)
        if json_content:
            return cls.from_json(json_content)
    @classmethod
    def get_by_ids(cls, ids):
        if not ids:
            return []
        results = cls.redis_client.hmget(cls._KEY, ids)
        return [cls.from_json(json_content)
                for json_content in results]
    @classmethod
    def get_next_id(cls):
        return MAX_ID.get_next_id(cls._KEY)
    def save(self):
        self._populate_default_attributes()
        self._save_self()
    def _populate_default_attributes(self):
        if self.id is None:
            self.id = self.get_next_id()
    def _save_self(self):
        self.redis_client.hset(self._KEY, self.id, self.to_json())
class MAX_ID(SimpleModel):
    @classmethod
    def get_next_id(cls, for_type, increment=1):
        return cls.redis_client.hincrby(cls._KEY, for_type, increment)
    @classmethod
    def get_max_id(cls, for_type):
        return int(cls.redis_client.hget(cls._KEY, for_type) or 0)

class IDModel(JSONModel):
    id = IntegerProperty()
    @classmethod
    def get_by_id(cls, entity_id):
        json_content = cls.redis_client.lindex(cls._KEY, entity_id)
        if json_content:
            return cls.from_json(json_content)
    @classmethod
    def get_by_ids(cls, ids):
        if not ids:
            return []
        key = cls._KEY
        pipe = cls.redis_client.pipeline(transaction=False)
        for entity_id in ids:
            pipe.lindex(key, entity_id)
        results = pipe.execute()
        return [cls.from_json(json_content)
                for json_content in results]
    def save(self):
        key = self._KEY
        if self.id is None:
            with self.redis_client.pipeline() as pipe:
                try:
                    pipe.watch(key)
                    self.id = pipe.llen(key) + 1
                    pipe.multi()
                    pipe.rpush(key, self.to_json())
                    pipe.execute()
                except Exception:
                    self.id = None
                    raise
        else:
            self.redis_client.lset(key, self.id, self.to_json())

1. ID 必须连续
   
2. 依赖事务，导致 _populate_default_attributes() 的逻辑不好分离
   
3. 获取多个 ID 对应的实体需要执行多条语句
   

原文地址：用 Redis 存储 ID 连续的数据, 感谢原作者分享。