ndb通过没有父节点的ID检索实体键 [英] ndb retrieving entity key by ID without parent

问题描述

我想获得一个知道实体ID和祖先的实体密钥。
ID在祖先定义的实体组内是唯一的。
在我看来，使用ndb接口是不可能的。就我所了解的数据存储而言，这可能是由于此操作需要完整的索引扫描才能执行。
我使用的解决方法是在模型中创建一个计算属性，该属性将包含密钥的id部分。我现在可以做一个祖先查询并获得关键字

$ $ p $ class $ SomeModel（$ b $）
ID = ndb.ComputedProperty（lambda self：self.key.id（））

@classmethod
def id_to_key（cls，identifier，祖先）：
返回cls.query cls.ID == identifier，
ancestor = ancestor.key）.get（keys_only = True）

它看起来可行，但是有没有更好的解决方案来解决这个问题？

更新
看起来对于数据存储自然的解决方案是使用完整路径而不是标识符。起初我认为这太繁重了。在阅读dragonx答案后，我重新设计了我的应用程序。令我惊奇的是，现在一切看起来都更简单了。额外的好处是，我的实体将使用更少的空间，我不需要额外的索引。

解决方案

我也遇到了这个问题。我认为你有解决方案。

更好的解决方案是停止使用ID来引用实体，并存储实际密钥或完整路径。

在内部，我使用键而不是ID。

在我的rest API中，我用 http：// url / kind / id （其中id看起来像123）来获取实体。我修改了它以提供实体的完整祖先路径： http：// url / kind / ancestor-ancestor-id （789-456-123），我会然后解析该字符串，生成一个密钥，然后按键。

I want to get an entity key knowing entity ID and an ancestor. ID is unique within entity group defined by the ancestor. It seems to me that it's not possible using ndb interface. As I understand datastore it may be caused by the fact that this operation requires full index scan to perform. The workaround I used is to create a computed property in the model, which will contain the id part of the key. I'm able now to do an ancestor query and get the key

class SomeModel(ndb.Model):
    ID = ndb.ComputedProperty( lambda self: self.key.id() )

    @classmethod
    def id_to_key(cls, identifier, ancestor):
        return cls.query(cls.ID == identifier,
                         ancestor = ancestor.key ).get( keys_only = True)

It seems to work, but are there any better solutions to this problem?

Update It seems that for datastore the natural solution is to use full paths instead of identifiers. Initially I thought it'd be too burdensome. After reading dragonx answer I redesigned my application. To my suprise everything looks much simpler now. Additional benefits are that my entities will use less space and I won't need additional indexes.

解决方案

I ran into this problem too. I think you do have the solution.

The better solution would be to stop using IDs to reference entities, and store either the actual key or a full path.

Internally, I use keys instead of IDs.

On my rest API, I used to do http://url/kind/id (where id looked like "123") to fetch an entity. I modified that to provide the complete ancestor path to the entity: http://url/kind/ancestor-ancestor-id (789-456-123), I'd then parse that string, generate a key, and then get by key.

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