#35021: Debug query capturing on psycopg3 disregards execute wrappers
-------------------------------------+-------------------------------------
Reporter: Ran | Owner: nobody
Benita |
Type: Bug | Status: new
Component: Database | Version: 5.0
layer (models, ORM) |
Severity: Normal | Keywords:
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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== Problem
I use [https://docs.djangoproject.com/en/4.2/topics/db/instrumentation
/#connection-execute-wrapper connection.execute_wrapper] as a way to add
comments to certain queries (see code at the end for reference). And I
test the wrapper using `assertNumQueries` (see code at end for reference).
Once I switched from psycopg2 to psycopg3, this test started failing: the
unmodified query is captured, instead of the query modified by the execute
wrapper. Note however that the modified query is what is actually sent to
the DB, so this is only a debug issue.
I expect it's the same for `django.db.backends` debug logs but I haven't
verified this.
== Analysis
I've traced the issue to the following code in
`postgresql.DatabaseOperations.last_executed_query`
https://github.com/django/django/blob/66d58e77de3196404e0820a6fef0a6144186015a/django/db/backends/postgresql/operations.py#L296-L311:
{{{
#!python
if is_psycopg3:
def last_executed_query(self, cursor, sql, params):
try:
return self.compose_sql(sql, params)
except errors.DataError:
return None
else:
def last_executed_query(self, cursor, sql, params):
# https://www.psycopg.org/docs/cursor.html#cursor.query
# The query attribute is a Psycopg extension to the DB API
2.0.
if cursor.query is not None:
return cursor.query.decode()
return None
}}}
psycopg2 uses `cursor.query` which ends up being the modified query.
psycopg3 uses whatever's passed in which ends up being the unmodified
query.
It seems like psycopg3 has an equivalent in
[https://www.psycopg.org/psycopg3/docs/api/cursors.html#psycopg.Cursor._query
cursor._query]. It is documented in the API reference but with a warning
"You shouldn’t consider it part of the public interface of the object: it
might change without warnings. [...] If you would like to build reliable
features using this object, please get in touch so we can try and design
an useful interface for it.". So if this is the desired solution, will
need to work with psycopg to expose a stable interface.
== Reproduction code
Example execute wrapper:
{{{
#!python
def db_comment_wrapper(comment: str) -> AbstractContextManager[None]:
def handler(execute, sql, params, many, context):
clean_comment = escape(comment)
return execute(f'/* {clean_comment} */ {sql}', params, many,
context)
return db_connection.execute_wrapper(handler)
}}}
Test:
{{{
#!python
with self.assertNumQueries(1) as captured:
with db_comment_wrapper('This is a comment'):
list(ContentType.objects.all())
sql = captured[0]['sql']
assert sql.startswith('/* This is a comment */')
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/35021>
Django <https://code.djangoproject.com/>
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