Google App Engine中的自引用ReferenceProperty [英] Self-referential ReferenceProperty in Google App Engine

问题描述

有趣的是，我试图建立一个文件夹/文件夹模型，文件系统，但无法获取文件夹引用文件夹。

我的第一次尝试是这样的：

  class Folder（db.Model）：
 id = db.StringProperty（）
 name = db.StringProperty（）
 created = db.DateTimeProperty（auto_now_add = True ）
 folder = db.ReferenceProperty（Folder，collection_name =folders）
  

但那失败，因为当试图定义文件夹时未定义文件夹。

我也尝试在主要声明之外定义文件夹，如下所示：

  class Folder（db.Model）：
 id = db.StringProperty（）
 name = db.StringProperty（）
 created = db.DateTimeProperty（auto_now_add = True）
 
 Folder.folder = db.ReferenceProperty（Folder，collection_name =folder s）
  

但是失败的原因是：
AttributeError：'Folder'对象没有任何属性'folders'

我很难过。有没有人有此经验，或解决这个问题？

方案

这正是 SelfReferenceProperty

a>是为。

I'm having a bit of trouble with ReferencePropertys in App Engine (Python).

For a bit of fun, I'm trying to model a folder/file system, but having trouble getting folders to reference folders.

My first attempt was this:

class Folder(db.Model):
    id = db.StringProperty()
    name = db.StringProperty()
    created = db.DateTimeProperty(auto_now_add=True)
    folder = db.ReferenceProperty(Folder, collection_name="folders")

But that fails as "Folder" isn't defined when "folder" is trying to be defined.

I've also tried defining "folder" outside of the main declaration for "Folder", like so:

class Folder(db.Model):
    id = db.StringProperty()
    name = db.StringProperty()
    created = db.DateTimeProperty(auto_now_add=True)

Folder.folder = db.ReferenceProperty(Folder, collection_name="folders")

But that fails with: AttributeError: 'Folder' object has no attribute 'folders'

I'm kind of stumped. Does anyone have experience with this, or a solution to this problem?

Thanks in advance.

解决方案

That's exactly what SelfReferenceProperty is for.

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