[Zope-DB] rollback / commit inside DTML : How To ??
Matthew T. Kromer
Mon, 07 Oct 2002 13:41:06 -0400
Federico Di Gregorio wrote:
>Il lun, 2002-10-07 alle 18:43, Harald Koschinski ha scritto:
>>does anybody know, howto commit / rollback a DB-transaction inside a DTML-Script by hand.
>>I know the python functions (get_transaction().commit() ...) but how can I call
>*don't* *call* *them*. (zope does it for you and you will only mess with
>the transaction system..)
Agreed -- dont try to abort or commit the transaction *during* the
transaction. You'll get in a world of hurt if you try.
Instead, what you might want to consider doing is registering a callback
object with the transaction manager.
Take a look at the Shared.DC.ZRDB.TM's TM class. It implements a
transaction manager (which has a naming 'misfeature' or two IMHO).
What you might want to do is something like:
def __init__(self, datum):
""" initialize with some data, useful for remembering """
def tpc_vote(self, context):
""" Called *before* commit """
self._finalize = 1 # Have to borrow this from the underlying
""" Called when we're to commit """
# commit ourselves to DB or whatever
""" Called when we're to abort """
# abort ourself to DB or whatever
You can instantiate a monitor then to hang around through the course of
the transaction and do something if the transaction is commited/aborted,
or use the vote hook to get an opportunity to call an abort (by raising
an exception) if some condition isnt to your liking.
However, trying to call a commit early is a mistake. Consider the
DEBIT your_account some_amount
CREDIT your_other_account some_amount
**** ERROR: your_other_account does not exist!
Uh, if the credit blows up, your money poofed. You dont want that. One
element of a transaction doesn't have any knowledge of what else may
happen subseqently in the transaction, so you *really* dont want to try
to commit early.
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