I have a set of entities all of the same kind, AnalyticsCounter, in my
datastore. For correctness I would like to update many of these entities in
a single transaction, which requires they are all in the same entity group.
In my case I don't have a hierarchy, instead I just have a set of entities.
My understanding is that I need to parent all of them to another
AnalyticsCounter entity to achieve this. However when I tried this, I
received the fateful "Cannot operate on different entity groups in a
transaction error.".
I created the parent entity in my constructor, and then applied the parent
when I created an instance of AnalyticsCounter, but the transaction fails on
the put method. Interestingly the "different entity groups" lists both the
newly created instance and the parent instance. I tried creating the parent
two different ways, first just creating a key:
self._parent_key = db.Key.from_path('AnalyticsCounter', 'virtual_root')
and then, creating an actual instance.
self._parent_instance = AnalyticsCounter.get_or_insert(key_name='root')
but met the same failure on both cases.
Briefly, my transaction looks like this:
counters = [list of key_names]
def txn():
counters = AnalyticsCounter.get_by_key_name(counters)
for counter in counters:
if counter is None:
counter = AnalyticsCounter(parent=self._parent_instance,
key_name='blah')
counter.foo = 'bar'
counter.put() # <- dies here
db.run_in_transaction(txn)
Can someone shed some light on what I am doing wrong? Thanks,
Chris
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