Neat way to remove obsolete properties from entities?

[Greg]

I've stumbled across what looks like a neat way to remove obsolete
properties from entities, without having to switch models to Expando
and back again. I convert the entity to a protocol buffer, which
reveals the obsolete properties. Then I remove them, convert back to
an entity and save it.

So far my testing has shown this doesn't have any ill effects, but I'd
like feedback in case what I'm doing is dangerous. In particular, I
don't understand what would happen to the indexes for the removed
properties - how does the datastore handle these?

Cheers
Greg.

# !!! EXPERIMENTAL CODE !!!
# !!! USE ENTIRELY AT YOUR OWN RISK !!!
# !!! NOT ENDORSED BY GOOGLE (YET) !!!

from google.appengine.ext import db

def remove_stale_properties(e):
current_properties=e.properties().keys()
epb=db.model_to_protobuf(e)
for i in reversed(range(len(epb.property_))):
if epb.property_[i].name() not in current_properties:
logging.info('Deleting property %s:%s'%
(epb.property_[i].name(),epb.property_[i].value()))
del epb.property_[i]
for i in reversed(range(len(epb.raw_property_))):
if epb.raw_property_[i].name() not in current_properties:
logging.info('Deleting raw property %s:%s'%
(epb.raw_property_[i].name(),epb.raw_property_[i].value()))
del epb.raw_property_[i]
return db.model_from_protobuf(epb)

# Example usage

entity_list=Foo.all().fetch(1000)
for entity in entity_list:
entity=remove_stale_properties(entity)
db.put(entity_list)

[Robert Kluin]

Hey Greg,
Assuming you are deleting the property definition from the Model,
then I think you can also use:

your_entity._entity.pop('property_to_delete', None)

It is shorter, and probably a little clearer.

Robert

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[Erwin Streur]

Robert,

Are you sure that this is going to work? In GAE there is a significant
difference between a property not being set/not existing at all and
being set to null/None.

Erwin

> > For more options, visit this group athttp://groups.google.com/group/google-appengine?hl=en.- Tekst uit oorspronkelijk bericht niet weergeven -
>
> - Tekst uit oorspronkelijk bericht weergeven -

[Robert Kluin]

Hey Erwin,
Try it. Here's some sample code:

class T(db.Model):
sp = db.StringProperty()
ip = db.IntegerProperty()

T(key_name='test', sp='some str', ip=7).put()

# stop. go look in the datastore viewer.
# now, comment out the def of 'sp' and the put(), then rerun with
test_t = T.get_by_key_name('test')
test_t._entity.pop('sp', None)
test_t.put()

Robert