id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
12180	ProgrammingError thrown with autocommit: True if first query on PostgreSQL >= 8.2 is an INSERT	Christophe Pettus	Christophe Pettus	"There is a bug in the handling of InsertQuery.connection.features.can_return_id_from_insert, which is causing Django 1.1.1 to throw a ProgrammingError exception when inserting a new object/record into the database, using PostgreSQL 8.4.1, using psycopg2, if that INSERT is the first thing done by a view on a particular connection to the database, when DATABASE_OPTIONS autocommit: True is set.

The details are:

1. Django uses InsertQuery.connection.features.can_return_id_from_insert to decide whether or not append a RETURNING clause to the INSERT, so that it can get the primary key of a newly-inserted object (db/models/sql/subqueries.py, lines 311-315).

2. That flag is set in the _cursor method of DatabaseWrapper (db/backends/postgresql_psycopg2/base.py, lines 106-121), but the cursor hasn't been created yet in step #1, so can_return_id_from_insert is always False.

3. But Django then issues the query (creating the cursor, and correctly setting can_return_id_from_insert to True), and thus expects a return value to come back the INSERT statement, but since the RETURNING clause wasn't added in step #1, it throws a ProgrammingError exception when it tries to get the expected return value (db/models/sql/subqueries.py, lines 323-324).

This appears to be a bad interaction with autocommit: True, since the code is clearly expecting a transaction to already have been opened at this point, which would have set the version information and the can_return_id_from_insert to True.
"	Bug	closed	Database layer (models, ORM)	1.3	Normal	fixed		brett@…	Accepted	1	0	1	0	0	0