I am trying find pattern avoiding circular import in Python Google App Engine Ndb datastore architecture. I want to have separate files which parent mode and children models (related to parent).
Only option which I found is to join parent and children into one file but it make code too complicated and not easy to scale (add more lines).
Currently I have such project structure.
parent.py - parent entity
base.py - abstract base entity for children
children.py - children module
I was read this answer How to avoid circular imports in Python? and trying to use but without success it is O.K. with typical Python objects but not works with initialized ndb properties. I spend some hours but has no idea why it is not works.
parent.py (need children for delete dependencies)
import children
from google.appengine.ext import ndb
class Parent(ndb.Model):
def deleteWithChildren(self):
for child in children.Child.query(Child.parent == self.key).fetch():
child.key.delete()
self.key.delete()
base.py (need parent for Reference)
from google.appengine.ext import ndb
import parent
class BaseChild(ndb.Model):
parent = ndb.KeyProperty(kind=parent.Parent)
children.py (need base do need Parent too)
import base
class Child(base.BaseChild):
pass
It produce exception when I try to execute such code import Parent:
File "sandbox\sandbox.py", line 6, in <module>
from web_site.seo.frontend.sandbox.parent import Parent
File "sandbox\parent.py", line 4, in <module>
import children
File "sandbox\children.py", line 4, in <module>
import base
File "sandbox\base.py", line 7, in <module>
class BaseChild(ndb.Model):
File "sandbox\base.py", line 8, in BaseChild
parent = ndb.KeyProperty(model=parent.Parent)
AttributeError: 'module' object has no attribute 'Parent'
