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Asked: 2026-06-12T20:19:19+00:00

I have a question about updating field in GAE database. My problem looks like

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I have a question about updating field in GAE database. My problem looks like this:

class A(db.Model):
    a = db.StringProperty()

and I added bool field:

class A(db.Model):
    a = db.StringProperty()
    b = db.BooleanProperty(default=False)

Now my problem is I’d like to have every instance of model b == False.

To update it I could of course drag them out of datastore and put them back there, but there is 700k elements there already and I really don’t know how to do it efficiently. I can’t take them out at once because I get soft memory exceeded errors. If I try to do it with little chunks – it costs me many db read operations. Do you have any idea how else I could update my datastore?

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1 Answer

  1. Editorial Team

    I agree with @ShayErlichmen. However, if you really want to update every entity, the easiest way is to use the MapReduce library:
    http://code.google.com/p/appengine-mapreduce/

    It’s not as easy as it sounds, because the documentation sucks, but this is the getting started point:
    http://code.google.com/p/appengine-mapreduce/wiki/GettingStartedInPython

    You just write a function foo() that will check the value of each entity passed to it, and if necessary, write update the value of your Boolean, and write it.

    The library will grab batches of entities and send each batch to a separate task. Each task will run in a loop calling your function foo(). Note that the batches run in parallel, so it may launch a few instances in parallel, but it tends to be quick.

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