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)
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