Cannot operate on a closed cursor error

[lkraav]

2009-12-16 14:26:35,474 Trac[chrome] DEBUG: Prepare chrome data for request
2009-12-16 14:26:35,478 Trac[model] DEBUG: get_pastes() SQL: 'SELECT id, title, author, time FROM pastes ORDER BY id DESC LIMIT 10' (None)
2009-12-16 14:26:35,599 Trac[main] ERROR: Internal Server Error:
Traceback (most recent call last):
  File "/secure/trac/virtual-0.11/trac-src/trac/web/main.py", line 450, in _dispatch_request
    dispatcher.dispatch(req)
  File "/secure/trac/virtual-0.11/trac-src/trac/web/main.py", line 206, in dispatch
    resp = chosen_handler.process_request(req)
  File "build/bdist.linux-i686/egg/tracpaste/web_ui.py", line 141, in process_request
    'recent':           get_pastes(env=self.env, number=self.max_recent)
  File "build/bdist.linux-i686/egg/tracpaste/model.py", line 53, in get_pastes
    cursor.execute(sql, where_values)
  File "/secure/trac/virtual-0.11/trac-src/trac/db/util.py", line 65, in execute
    return self.cursor.execute(sql)
  File "/secure/trac/virtual-0.11/trac-src/trac/db/sqlite_backend.py", line 80, in execute
    PyFormatCursor.execute(self, *args)
  File "/secure/trac/virtual-0.11/trac-src/trac/db/sqlite_backend.py", line 59, in execute
    args or [])
  File "/secure/trac/virtual-0.11/trac-src/trac/db/sqlite_backend.py", line 51, in _rollback_on_error
    return function(self, *args, **kwargs)
ProgrammingError: Cannot operate on a closed cursor.

[lkraav]

this could be related to #6302.

[Ryan J Ollos]

#7138 was closed as a duplicate.

[Ryan J Ollos]

Isn't this (source:tracpasteplugin/0.11/tracpaste/model.py@4949#L31​)

cursor = (db or env.get_db_cnx()).cursor()

just as bad of a practice as?:

cursor = env.get_db_cnx().cursor

Shouldn't we replace that code with?:

db = (db or env.get_db_cnx())
cursor = db.cursor()

Per ​t:wiki:TracDev/DatabaseApi#APIbeforeTrac0.12

[Ryan J Ollos]

Since I have TracPastePlugin setup in a dev environment following #8298, I'd be happy to apply the proposed fix for this as well, given permission of the maintainer.

0.11/tracpaste/model.py

@@ -28 +28 @@
 
     To get the paste data, use id to instantiate a Paste object."""
 
-    cursor = (db or env.get_db_cnx()).cursor()
+    db = db or env.get_db_cnx()
+    cursor = db.cursor()
 
     sql = "SELECT id, title, author, time FROM pastes"
     order_clause = " ORDER BY id DESC"

[Ryan J Ollos]

#6361 closed as a duplicate.

[osimons]

Patch looks good to me.

[Michael Renzmann]

No objections from me. Feel free to commit.

[Ryan J Ollos]

(In [9678]) Attempt to resolve reported closed cursor error by making sure db object does not get removed up by Python. Version bumped to 0.2.2. Fixes #6341.