Hi there,
I am working with SqlAlchemy for the first time (coming from
SqlObject), and I fear I may not understand it as well as I thought I
did...
I have a class (X), persisted with SA which contains a key (X.key)
which is a randomly generated string of fixed length. This field is
supposed to be unique as well.
When you create a X, though, there is the chance that the newly
generated key may clash with an existing one in the DB. In which case
I'd like to regenerate the random key and try again. But, you cannot
use a sequence in the DB for generating the key, since it should be
random, but unique.
Naïvely, I thought you'd create an X, flush it, and then catch any
IntegrityError's thrown. Something like:
session.begin()
#create some other objects
unique = False
#session.begin()
while not unique:
try:
newx = X() # It generates its own random key in the __init__
session.save(newx)
session.flush()
unique = True
except IntegrityError:
pass
#session.commit()
session.commit()
But, this does not work: It seems that the whole transaction is rolled
back when the IntegrityError happens, so objects created before this
code is then lost here. Ive tried putting a nested transaction around
this bit of code (using session.begin/commit as indicated in
comments), but that did not work.
This is done with SqlAlchemy 0.4 (and Elixir 0.5), on postgresql 8.3.
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