Self-referential ReferenceProperty in Google App Engine
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?
开发者_如何学编程Thanks in advance.
That's exactly what SelfReferenceProperty is for.
You could create a separate model to link the two, named something like FolderChild:
class FolderChild(db.Model):
parent = db.ReferenceProperty(Folder)
child = db.ReferenceProperty(Folder, collection_name="children")
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