Hi David,
Depends how you define easy. You'll need to loop over the data,
convert it, then re-put it. There are a couple ways to do this, but I
think the easiest to explain is the 'Expando two-step' method. First,
change your kind definition to the new schema (including removing the
old properties) also switch from a db.Model to a db.Expando. Then
loop over your entities, for each entity copy the value from the old
property to the new property, then db.put your entities. Change your
kind back to a db.Model.
I'd also suggest adding a 'version' property to your kind definition
to make this sort of thing easier in the future. Personally, I stick
a "v_ = IntegerProperty(default=0)" on all of my kinds then bump the
default each time I modify the schema. Makes finding stuff that needs
updated super easy.
There are several choices for how you loop over your data. The
write a handler and use task-queues, use task-queues plus deferred, or
use the map-reduce lib. The first method is pretty easy to outline:
def get(self):
query = KindToMigrate.all()
cursor = self.request.get('cursor')
if cursor:
query.with_cursor(cursor)
entities = query.fetch(batch_size) # maybe a couple hundred
if len(entities) >= batch_size:
taskqueue.add(url=self.request.path,
params={'cursor': str(query.cursor())})
for entity in entities:
if hasattr(entity, 'old_property'):
entity.np = entity.old_property
delattr(entity, 'old_property')
db.put(entities)
I'd carefully review and test the before running it since I just
quickly typed it up. ;)
Robert
On Mon, May 30, 2011 at 17:18, David Stone <minpeng2...@gmail.com> wrote:
> Hello,
>
> Suppose i have a kind (table) called "Person" defined in GAE data
> store already, it has properties (attributes) like personId, age,
> location, phone number and contains one million tuples. Now i just
> want to change attribute "personId" to "pId" without affect anything
> else.
>
> Is there any easy way to do so?
>
> Thanks!
>
> David
>
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