django.db.backends.BaseDatabaseOperations.last_executed_query can raise an exception

[a.gerchenov@…]

Method "last_executed_query" should not always return "smart_unicode(sql) % u_params". If params variable is empty it should return just "smart_unicode(sql)". The problem is when we try to execute query with MySQL DATA_FORMAT function it says error.

Example:

from django.db import connection
c = connection.cursor()
c.execute("SELECT * FROM VAR_current GROUP BY DATE_FORMAT(closing_month, '%Y-%m');")
print c.fetchall()

Error:

django/db/backends/__init__.py", line 216, in last_executed_query
    return smart_unicode(sql) % u_params
TypeError: not enough arguments for format string

This issue is closely related to #9055.

[Aymeric Augustin]

Since r16081, there is a better implementation of last_executed_query for MySQL (and Oracle), so the problem is solved as far as MySQL is concerned.

It still exists for SQLite, and although we came to the conclusion that we couldn't build a reliable last_executed_query for SQLite in #14091, it shouldn't raise an exception.

I see three possible solutions:

• 1) give up on interpolation entirely, and return a string like "SQL = ..., PARAMS = ...".
• 2) catch exceptions in the interpolation and return smart_unicode(sql) if an exception occurs
• 3) mangle the SQL to replace some % by %% before interpolation.

I'm in favor of 1 because it will avoid returning subtly invalid SQL when the database backend in SQLite. It's backwards incompatible, but last_executed_query never returned something usable under SQLite. Returning obviously incomplete SQL is less likely to confuse newcomers.

I'm against 3 because it's overengineering, and I'm not convinced it's possible to get it right for all cases anyway.

[Aymeric Augustin]

I've just uploaded a test case demonstrating the issue under SQLite. The assertion in this test case may have to be changed depending on the solution that we actually choose.

[Aymeric Augustin]

I'll commit the patch I just attached if no one objects.

[Anssi Kääriäinen]

looks good.

[Aymeric Augustin <aymeric.augustin@…>]

In 6605ac331a9e03fa41c301d122c5727c0d98b970:

Fixed #17158 -- Used a non-ambiguous representation of SQL queries

when a correct representation cannot be obtained.