To remove deleted properties from the datastore, GAE docs suggest this:
https://developers.google.com/appengine/articles/update_schema
It boils down to re-defining your class hierarchy as Expando, fetch, call
delattr, put, then changing model back.
What I've noticed is that even when you remove a property from your model,
you can still see the type and value in `_properties` and `_values`
properties on the object.
tl;dr - If I just remove it from those internal dicts and save, it seems
to work - that's a lot easier than what the docs above suggest -- is it
safe to do?
--
Full example showing what I mean:
Try this at shell.appspot.com: create an entity with a couple properties.
>>> class Foo(ndb.Model):
s = ndb.StringProperty()
s2 = ndb.StringProperty()
>>> f = Foo(id="foo", s="this is s1", s2="this is s2")
>>> f.put()
Then re-define the class without one of the props, and fetch the object
back:
>>> class Foo(ndb.Model):
s = ndb.StringProperty()
>>> g = Foo.get_by_id("foo")
Trying to access the deleted property directly will give you an
AttributeError, as you'd expect:
>>> g.s2
Traceback (most recent call last):
File "/base/data/home/apps/shell/1.335852500710379686/shell.py", line
267, in get
exec compiled in statement_module.__dict__
File "<string>", line 1, in <module>
AttributeError: 'Foo' object has no attribute 's2'
But you can still "see" the remove property in the _properties and _values
arrays:
>>> g._properties
{'s2': GenericProperty('s2', repeated=0), 's': StringProperty('s')}
>>> g._values
{'s2': _BaseValue('this is s2'), 's': _BaseValue('this is s1')}
And -- this is the important part -- if you remove it from those internal
dicts and put(),
>>> del g._properties["s2"]
>>> del g._values["s2"]
>>> g.put()
it appears to remove the property from the datastore, and it's completely
gone when you re-fetch:
>>> h = Foo.get_by_id("foo")
>>> h._properties
{'s2': GenericProperty('s2', repeated=0), 's': StringProperty('s')}
This is a *a lot *easier than redefining models, uploading new versions,
then changing them back, re-uploading, etc.
Much rather just reach into the object, del the stale property and save.
Does anyone know if this is safe? Am I asking for trouble if I start to
clean up stale properties using this method?
Thanks for any answers, comments.
-ck
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