Hi Mike,
thanks for the quick response.

These would be the debug logs for

import requests
for i in range(2):
    r = requests.put('http://0.0.0.0:8080/update-datetime')
    print(r.text, r.code)

2023-09-01 16:06:20,711 INFO sqlalchemy.engine.Engine SELECT DATABASE()
2023-09-01 16:06:20,711 INFO sqlalchemy.engine.Engine [raw sql] ()
2023-09-01 16:06:20,713 DEBUG sqlalchemy.engine.Engine Col ('DATABASE()',)
2023-09-01 16:06:20,713 DEBUG sqlalchemy.engine.Engine Row ('dbname',)
2023-09-01 16:06:20,714 INFO sqlalchemy.engine.Engine SELECT @@sql_mode
2023-09-01 16:06:20,714 INFO sqlalchemy.engine.Engine [raw sql] ()
2023-09-01 16:06:20,715 DEBUG sqlalchemy.engine.Engine Col ('@@sql_mode',)
2023-09-01 16:06:20,715 DEBUG sqlalchemy.engine.Engine Row 
('ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION',)
2023-09-01 16:06:20,716 INFO sqlalchemy.engine.Engine SELECT 
@@lower_case_table_names
2023-09-01 16:06:20,716 INFO sqlalchemy.engine.Engine [raw sql] ()
2023-09-01 16:06:20,717 DEBUG sqlalchemy.engine.Engine Col 
('@@lower_case_table_names',)
2023-09-01 16:06:20,717 DEBUG sqlalchemy.engine.Engine Row (0,)
2023-09-01 16:06:20,717 INFO sqlalchemy.engine.Engine BEGIN (implicit)
2023-09-01 16:06:20,719 INFO sqlalchemy.engine.Engine SELECT foo.id AS 
foo_id, foo.last_login AS foo_last_login, foo.name AS foo_name
FROM foo
WHERE foo.id = %s
 LIMIT %s
2023-09-01 16:06:20,719 INFO sqlalchemy.engine.Engine [generated in 
0.00016s] (1, 1)
2023-09-01 16:06:20,720 DEBUG sqlalchemy.engine.Engine Col ('foo_id', 
'foo_last_login', 'foo_name')
2023-09-01 16:06:20,720 DEBUG sqlalchemy.engine.Engine Row (1, 
datetime.datetime(2023, 9, 1, 16, 6, 12), '2023-09-01 15:50:46.029445')
2023-09-01 16:06:20,722 INFO sqlalchemy.engine.Engine UPDATE foo SET 
last_login=%s WHERE foo.id = %s
2023-09-01 16:06:20,722 INFO sqlalchemy.engine.Engine [generated in 
0.00014s] (datetime.datetime(2023, 9, 1, 16, 6, 20, 721146), 1)
2023-09-01 16:06:20,723 INFO sqlalchemy.engine.Engine COMMIT
192.168.0.1 - - [01/Sep/2023 16:06:20] "PUT /update-datetime HTTP/1.1" 200 -
2023-09-01 16:06:20,733 INFO sqlalchemy.engine.Engine BEGIN (implicit)
2023-09-01 16:06:20,733 INFO sqlalchemy.engine.Engine SELECT foo.id AS 
foo_id, foo.last_login AS foo_last_login, foo.name AS foo_name
FROM foo
WHERE foo.id = %s
 LIMIT %s
2023-09-01 16:06:20,733 INFO sqlalchemy.engine.Engine [cached since 
0.01402s ago] (1, 1)
2023-09-01 16:06:20,734 DEBUG sqlalchemy.engine.Engine Col ('foo_id', 
'foo_last_login', 'foo_name')
2023-09-01 16:06:20,735 DEBUG sqlalchemy.engine.Engine Row (1, 
datetime.datetime(2023, 9, 1, 16, 6, 21), '2023-09-01 15:50:46.029445')
2023-09-01 16:06:20,736 INFO sqlalchemy.engine.Engine UPDATE foo SET 
last_login=%s WHERE foo.id = %s
2023-09-01 16:06:20,736 INFO sqlalchemy.engine.Engine [cached since 
0.01399s ago] (datetime.datetime(2023, 9, 1, 16, 6, 20, 735704), 1)
2023-09-01 16:06:20,737 INFO sqlalchemy.engine.Engine ROLLBACK
192.168.0.1 - - [01/Sep/2023 16:06:20] "PUT /update-datetime HTTP/1.1" 500 -
Traceback (most recent call last):
  File "/usr/local/lib/python3.8/site-packages/flask/app.py", line 2548, in 
__call__
    return self.wsgi_app(environ, start_response)
  File "/usr/local/lib/python3.8/site-packages/flask/app.py", line 2528, in 
wsgi_app
    response = self.handle_exception(e)
  File "/usr/local/lib/python3.8/site-packages/flask/app.py", line 2525, in 
wsgi_app
    response = self.full_dispatch_request()
  File "/usr/local/lib/python3.8/site-packages/flask/app.py", line 1822, in 
full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/usr/local/lib/python3.8/site-packages/flask/app.py", line 1820, in 
full_dispatch_request
    rv = self.dispatch_request()
  File "/usr/local/lib/python3.8/site-packages/flask/app.py", line 1796, in 
dispatch_request
    return self.ensure_sync(self.view_functions[rule.endpoint])(**view_args)
  File "/usr/src/app/sqa.py", line 69, in update_datetime
    db_session.commit()
  File "<string>", line 2, in commit
  File "/usr/local/lib/python3.8/site-packages/sqlalchemy/orm/session.py", 
line 1454, in commit
    self._transaction.commit(_to_root=self.future)
  File "/usr/local/lib/python3.8/site-packages/sqlalchemy/orm/session.py", 
line 832, in commit
    self._prepare_impl()
  File "/usr/local/lib/python3.8/site-packages/sqlalchemy/orm/session.py", 
line 811, in _prepare_impl
    self.session.flush()
  File "/usr/local/lib/python3.8/site-packages/sqlalchemy/orm/session.py", 
line 3449, in flush
    self._flush(objects)
  File "/usr/local/lib/python3.8/site-packages/sqlalchemy/orm/session.py", 
line 3589, in _flush
    transaction.rollback(_capture_exception=True)
  File 
"/usr/local/lib/python3.8/site-packages/sqlalchemy/util/langhelpers.py", 
line 70, in __exit__
    compat.raise_(
  File "/usr/local/lib/python3.8/site-packages/sqlalchemy/util/compat.py", 
line 211, in raise_
    raise exception
  File "/usr/local/lib/python3.8/site-packages/sqlalchemy/orm/session.py", 
line 3549, in _flush
    flush_context.execute()
  File 
"/usr/local/lib/python3.8/site-packages/sqlalchemy/orm/unitofwork.py", line 
456, in execute
    rec.execute(self)
  File 
"/usr/local/lib/python3.8/site-packages/sqlalchemy/orm/unitofwork.py", line 
630, in execute
    util.preloaded.orm_persistence.save_obj(
  File 
"/usr/local/lib/python3.8/site-packages/sqlalchemy/orm/persistence.py", 
line 237, in save_obj
    _emit_update_statements(
  File 
"/usr/local/lib/python3.8/site-packages/sqlalchemy/orm/persistence.py", 
line 1035, in _emit_update_statements
    raise orm_exc.StaleDataError(
sqlalchemy.orm.exc.StaleDataError: UPDATE statement on table 'foo' expected 
to update 1 row(s); 0 were matched.

On Friday, September 1, 2023 at 7:02:56 PM UTC+3 Mike Bayer wrote:

> a stale data error with date/time fields is usually a mismatch between the 
> date/time value you have locally and the one that's in the database,. 
> assuming you are using the datetime column as a "version_id" in your 
> mapping.     Issues like strings vs. datetimes and/or microseconds portions 
> being present or non-present are the most common.
>
> would need to see SQL debug logging to have more insight / confirm that's 
> the problem.
>
> On Fri, Sep 1, 2023, at 11:59 AM, Dumitru Gîra wrote:
>
> I have encountered a very strange behaviour and I don't know where to look 
> further.
> I have a small API https://pastebin.com/qW01jNz8 with 2 endpoints: one to 
> update the name (VARCHAR) and one to update the last_login (DATETIME).
>
> If I make 10 consecutive requests to /update-string - everything works as 
> expected.
> If I make 10 consecutive requests to /update-datetime - the first request 
> works and other 9 fail with sqlalchemy.orm.exc.StaleDataError.
> NOTE: putting a time.sleep(1) after every request does not raise the error
>
> Consecutive requests are being made using the simple snippet
> import requests
> for i in range(10):
>     r = requests.put('http://0.0.0.0:8080/update-datetime')
>     print(r.text, r.code)
>
> The source code and the logs are in above link and for the reference I am 
> using:
> - MySQL 8.0, but the same happens with 5.7
> - mysqldb connector, but the same happens with pymysql
> - SQLAlchemy==1.4.49
>
> Is this related to MySQL and specifically to date/time related fields (as 
> the same happens with TIMESTAMP) or can it be something from SQLAlchemy 
> side?
> Any directions would be highly appreciated.
>
> Kind regards,
> Dumitru
>
>
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> The Python SQL Toolkit and Object Relational Mapper
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> http://www.sqlalchemy.org/
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http://www.sqlalchemy.org/

To post example code, please provide an MCVE: Minimal, Complete, and Verifiable 
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