Date: Sat, 7 Sep 2024 22:45:24 +0200
From: Karsten Hilbert <Karsten.Hilbert@gmx.net>
To: Adrian Klaver <adrian.klaver@aklaver.com>
Cc: psycopg@lists.postgresql.org, python-list@python.org
Subject: Re: psycopg2: proper positioning of .commit() within try: except:
 blocks
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Am Sat, Sep 07, 2024 at 01:03:34PM -0700 schrieb Adrian Klaver:

> In the case you show you are doing commit() before the close() so any er=
rors in the
> transactions will show up then. My first thought would be to wrap the co=
mmit() in a
> try/except and deal with error there.

Right, and this was suggested elsewhere ;)

And, yeah, the actual code is much more involved :-D

#------------------------------------------------------------------------
def __safely_close_cursor_and_rollback_close_conn(close_cursor=3DNone, rol=
lback_tx=3DNone, close_conn=3DNone):
	if close_cursor:
		try:
			close_cursor()
		except PG_ERROR_EXCEPTION as pg_exc:
			_log.exception('cannot close cursor')
			gmConnectionPool.log_pg_exception_details(pg_exc)
	if rollback_tx:
		try:
			# need to rollback so ABORT state isn't retained in pooled connections
			rollback_tx()
		except PG_ERROR_EXCEPTION as pg_exc:
			_log.exception('cannot rollback transaction')
			gmConnectionPool.log_pg_exception_details(pg_exc)
	if close_conn:
		try:
			close_conn()
		except PG_ERROR_EXCEPTION as pg_exc:
			_log.exception('cannot close connection')
			gmConnectionPool.log_pg_exception_details(pg_exc)

#------------------------------------------------------------------------
def run_rw_queries (
	link_obj:_TLnkObj=3DNone,
	queries:_TQueries=3DNone,
	end_tx:bool=3DFalse,
	return_data:bool=3DNone,
	get_col_idx:bool=3DFalse,
	verbose:bool=3DFalse
) -> tuple[list[dbapi.extras.DictRow], dict[str, int] | None]:
	"""Convenience function for running read-write queries.

	Typically (part of) a transaction.

	Args:
		link_obj: None, cursor, connection
		queries:

		* a list of dicts [{'cmd': <string>, 'args': <dict> or <tuple>)
		* to be executed as a single transaction
		* the last query may usefully return rows, such as:

			SELECT currval('some_sequence');
				or
			INSERT/UPDATE ... RETURNING some_value;

		end_tx:

		* controls whether the transaction is finalized (eg.
		  COMMITted/ROLLed BACK) or not, this allows the
		  call to run_rw_queries() to be part of a framing
		  transaction
		* if link_obj is a *connection* then "end_tx" will
		  default to False unless it is explicitly set to
		  True which is taken to mean "yes, you do have full
		  control over the transaction" in which case the
		  transaction is properly finalized
		* if link_obj is a *cursor* we CANNOT finalize the
		  transaction because we would need the connection for that
		* if link_obj is *None* "end_tx" will, of course, always
		  be True, because we always have full control over the
		  connection, not ending the transaction would be pointless

		return_data:

		* if true, the returned data will include the rows
		    the last query selected
		* if false, it returns None instead

		get_col_idx:

		* True: the returned tuple will include a dictionary
		    mapping field names to column positions
		* False: the returned tuple includes None instead of a field mapping dic=
tionary

	Returns:

		* (None, None) if last query did not return rows
		* ("fetchall() result", <index>) if last query returned any rows and "re=
turn_data" was True

		* for *index* see "get_col_idx"
	"""
	assert queries is not None, '<queries> must not be None'

	if link_obj is None:
		conn =3D get_connection(readonly =3D False)
		curs =3D conn.cursor()
		conn_close =3D conn.close
		tx_commit =3D conn.commit
		tx_rollback =3D conn.rollback
		curs_close =3D curs.close
		notices_accessor =3D conn
	else:
		conn_close =3D lambda *x: None
		tx_commit =3D lambda *x: None
		tx_rollback =3D lambda *x: None
		curs_close =3D lambda *x: None
		if isinstance(link_obj, dbapi._psycopg.cursor):
			curs =3D link_obj
			notices_accessor =3D curs.connection
		elif isinstance(link_obj, dbapi._psycopg.connection):
			if end_tx:
				tx_commit =3D link_obj.commit
				tx_rollback =3D link_obj.rollback
			curs =3D link_obj.cursor()
			curs_close =3D curs.close
			notices_accessor =3D link_obj
		else:
			raise ValueError('link_obj must be cursor, connection or None but not [=
%s]' % link_obj)

	for query in queries:
		try:
			args =3D query['args']
		except KeyError:
			args =3D None
		try:
			curs.execute(query['cmd'], args)
			if verbose:
				gmConnectionPool.log_cursor_state(curs)
			for notice in notices_accessor.notices:
				_log.debug(notice.replace('\n', '/').replace('\n', '/'))
			del notices_accessor.notices[:]
		# DB related exceptions
		except dbapi.Error as pg_exc:
			_log.error('query failed in RW connection')
			gmConnectionPool.log_pg_exception_details(pg_exc)
			for notice in notices_accessor.notices:
				_log.debug(notice.replace('\n', '/').replace('\n', '/'))
			del notices_accessor.notices[:]
			__safely_close_cursor_and_rollback_close_conn (
				curs_close,
				tx_rollback,
				conn_close
			)
			# privilege problem ?
			if pg_exc.pgcode =3D=3D PG_error_codes.INSUFFICIENT_PRIVILEGE:
				details =3D 'Query: [%s]' % curs.query.decode(errors =3D 'replace').st=
rip().strip('\n').strip().strip('\n')
				if curs.statusmessage !=3D '':
					details =3D 'Status: %s\n%s' % (
						curs.statusmessage.strip().strip('\n').strip().strip('\n'),
						details
					)
				if pg_exc.pgerror is None:
					msg =3D '[%s]' % pg_exc.pgcode
				else:
					msg =3D '[%s]: %s' % (pg_exc.pgcode, pg_exc.pgerror)
				raise gmExceptions.AccessDenied (
					msg,
					source =3D 'PostgreSQL',
					code =3D pg_exc.pgcode,
					details =3D details
				)

			# other DB problem
			gmLog2.log_stack_trace()
			raise

		# other exception
		except Exception:
			_log.exception('error running query in RW connection')
			gmConnectionPool.log_cursor_state(curs)
			for notice in notices_accessor.notices:
				_log.debug(notice.replace('\n', '/').replace('\n', '/'))
			del notices_accessor.notices[:]
			gmLog2.log_stack_trace()
			__safely_close_cursor_and_rollback_close_conn (
				curs_close,
				tx_rollback,
				conn_close
			)
			raise

	data =3D None
	col_idx =3D None
	if return_data:
		try:
			data =3D curs.fetchall()
		except Exception:
			_log.exception('error fetching data from RW query')
			gmLog2.log_stack_trace()
			__safely_close_cursor_and_rollback_close_conn (
				curs_close,
				tx_rollback,
				conn_close
			)
			raise

		if get_col_idx:
			col_idx =3D get_col_indices(curs)
	curs_close()
	tx_commit()
	conn_close()
	return (data, col_idx)

#------------------------------------------------------------------------


Best,
Karsten
=2D-
GPG  40BE 5B0E C98E 1713 AFA6  5BC0 3BEA AC80 7D4F C89B