On 07/19/2016 06:41 PM, Mike Bayer wrote:
On 07/19/2016 11:51 AM, TomS. wrote:
Hi,
We have Flask app which uses SQLAlchemy. Weird error started to happen
recently. The difficulty is that we can't reproduce the error (/figure
out conditions causing issue) - maybe someone could help. Any hints/tips
would be appreciated.
There is a part in the code which constructs IN in SQL:
MyModel.id.in_(my_ids)
For some cases my_ids is an empty list. It works without any problems,
but after some time the same query (using empty list) starts to raise an
exception:
SAWarning: The IN-predicate on "MyModel.id" was invoked with an empty
sequence. This results in a contradiction, which nonetheless can be
expensive to evaluate. Consider alternative strategies for improved
performance.
After restarting app, everything works again.
The question is - why this exception is not risen always (although we
tried to run app with empty list directly), but after some time of app
execution (~1 day)?
It's not an exception, it's a warning. Python warnings by default
emit only once, see:
https://docs.python.org/2/library/warnings.html#the-warnings-filter
Ok, this is the explanation why it doesn't show up regularly. Thank you.
I don't know why SAWarning is treated as error. Here is the log:
2016-07-21 13:58:14,108 ERROR: Exception on /own [GET]
Traceback (most recent call last):
[...]
File
"/home/developer/.virtualenvs/rest/lib/python2.7/site-packages/sqlalchemy/util/langhelpers.py",
line 1297, in warn
warnings.warn(msg, exc.SAWarning, stacklevel=2)
SAWarning: The IN-predicate on "MyModel.id" was invoked with an empty
sequence. This results in a contradiction, which nonetheless can be
expensive to evaluate.
I will also ask on Flask group, but maybe you know the reason - Flask
config regarding logging is as follow:
import logging
from logging.handlers import RotatingFileHandler
logger_file_handler = RotatingFileHandler('my.log', maxBytes=1024 * 1024
* 100, backupCount=20)
logger_file_handler.setLevel(logging.DEBUG)
logger_formatter = logging.Formatter(u'%(asctime)s %(levelname)s:
%(message)s')
logger_file_handler.setFormatter(logger_formatter)
logging.captureWarnings(True)
app.logger.addHandler(logger_file_handler)
app.logger.setLevel(logging.DEBUG)
There is no code which change behavior (by filter) of SAWarning to
'error' ...
Cheers
Details:
Flask==0.10.1
Flask-SQLAlchemy==2.1
SQLAlchemy==1.0.14
MySQL DB
Cheers
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