Django snippets: Nested commit_on

def nested_commit_on_success(func):
    """Like commit_on_success, but doesn't commit existing transactions.

    This decorator is used to run a function within the scope of a 
    database transaction, committing the transaction on success and
    rolling it back if an exception occurs.

    Unlike the standard transaction.commit_on_success decorator, this
    version first checks whether a transaction is already active.  If so
    then it doesn't perform any commits or rollbacks, leaving that up to
    whoever is managing the active transaction.
    """
    commit_on_success = transaction.commit_on_success(func)
    def _nested_commit_on_success(*args, **kwds):
        if transaction.is_managed():
            return func(*args,**kwds)
        else:
            return commit_on_success(*args,**kwds)
    return transaction.wraps(func)(_nested_commit_on_success)

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This is a simple modification to the standard transaction.commit_on_success decorator that is aware of existing transactions. If a managed transaction is already active then the wrapped function is called directly, assuming the active transaction will clean up as appropriate. Otherwise, a standard commit_on_success is performed.

I'm using this to wrap the save() method of models that manipulate other related models on save, e.g:

@nested_commit_on_success
def save(self):
    super(MyClass,self).save()
    for m in other_models:
        self.fix_up_other_model(m)
        m.save()

Author:: rfk
Posted:: February 26, 2009
Language:: Python
Django Version:: 1.0
Tags:: transaction
Score:: 2 (after 2 ratings)

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demichej (on August 10, 2011):

Thanks, RFK! I love it! I wonder why Django doesn't just use this decorator instead of its normal commit_on_success() what am I missing? It seems like this works exactly like commit_on_success, except it won't open a new transaction if one is already being managed?

demanzano (on August 11, 2011):

Very useful!

just a question, this code is for a decorator (the '@' operator) but what if I would use the 'with' operator ? How should I modify this code to be run with 'with' ? Thanks anyway !

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Nested commit_on_success

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