# mostly from JP
# added the functionality to run synchronious if there is already a active
# transaction
def _transact( engine ):
    """
    return a high level function bind to a particulary
    sqlalchemy engine

    this function is suitable to use as a decorator

    a decorated function returns a Deferred while its body
    is running in a separate thread
    """

    def _transaction( f ):
        # _transaction *is* the decorator
        def _wrap(*args, **kwargs):
            def _1():
                # either method works here now;
                # either contextual_connect()/begin()/trans.commit()
                # or engine.begin()/commit()
                conn = meta.engine.contextual_connect()
                trans = conn.begin()
                try:
                    r = f(*args, **kwargs)
                except:
                    trans.rollback()
                    conn.close()
                    raise
                else:
                    trans.commit()
                    conn.close()
                    return r
            if isInIOThread( ):
                return threads.deferToThread(_1)
            else:
                return _1( )
        _wrap.__name__ = f.__name__
        return _wrap
    return _transaction

transact = _transact( meta )