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Unable to get retry working with unique constraint failure. #313

neonquill opened this issue Nov 22, 2017 · 2 comments

Unable to get retry working with unique constraint failure. #313

neonquill opened this issue Nov 22, 2017 · 2 comments


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I haven't been able to figure out how to get the retry parameter to work correctly with database errors. I can reproduce the test code with ZeroDivisionError exceptions, but not with database errors (such as a unique constraint violation).

Test code:

#!/usr/bin/env python3

from pony import orm

db = orm.Database()

class Foo(db.Entity):
    unique = orm.Required(int, unique=True)

def retry_unique():

@orm.db_session(retry=3, retry_exceptions=[ZeroDivisionError])
def retry_zero_div():

def main():
    db.bind(provider='postgres', user='postgres', password='password',
            host='', database='test_retry')

        # This will run 4 times.

        # This will succeed (if db is empty).
        # This will only run once.  <- Bug?

if __name__ == '__main__':

Running this code on a clean database produces the following output:


I (correctly) see retry_zero_div() run 4 times (the first try plus the indicated 3 retries). For retry_unique() the first run succeeds (because there is no uniqueness violation) and then the second run throws an exception but is not re-tried (this seems wrong to me).

When I trace retry_zero_div() the retry gets caught in pony/pony/orm/ However, when I run retry_unique() the code never hits that line. This makes me think that it's not an issue of having the wrong exceptions in retry_exceptions.

At this point, I'm not entirely sure if I'm doing something wrong or there is really a bug. Any advice would be appreciated.

@kozlovsky kozlovsky added the bug label Nov 26, 2017
@kozlovsky kozlovsky self-assigned this Nov 26, 2017
@kozlovsky kozlovsky added this to the 0.7.4 milestone Nov 26, 2017
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Thanks for reporting! It was a bug.

Previous code for retry handling assumed that exception is raised inside a function. In your example, the exception was raised outside of the function, when db_session tried to save changes to the database. Now such exceptions are processed correctly too.

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Thanks for the fix and the explanation!

kozlovsky added a commit that referenced this issue Jul 23, 2018
# Major features

* Hybrid methods and properties added:
* Allow to base queries on another queries: `select(x.a for x in prev_query if x.b)`
* Added support of Python 3.7
* Added support of PyPy
* `group_concat()` aggregate function added
* pony.flask subpackage added for integration with Flask

# Other features

* `distinct` option added to aggregate functions
* Support of explicit casting to `float` and `bool` in queries

# Improvements

* Apply @cut_traceback decorator only when pony.MODE is 'INTERACTIVE'

# Bugfixes

* In SQLite3 `LIKE` is case sensitive now
* #249: Fix incorrect mixin used for Timedelta
* #251: correct dealing with qualified table names
* #301: Fix aggregation over JSON Column
* #306: Support of frozenset constants added
* #308: Fixed an error when assigning JSON attribute value to the same attribute: obj.json_attr = obj.json_attr
* #313: Fix missed retry on exception raised during db_session.__exit__
* #314: Fix AttributeError: 'NoneType' object has no attribute 'seeds'
* #315: Fix attribute lifting for JSON attributes
* #321: Fix KeyError on obj.delete()
* #325: duplicating percentage sign in raw SQL queries without parameters
* #331: Overriding __len__ in entity fails
* #336: entity declaration serialization
* #357: reconnect after PostgreSQL server closed the connection unexpectedly
* Fix Python implementation of between() function and rename arguments: between(a, x, y) -> between(x, a, b)
* Fix retry handling: in PostgreSQL and Oracle an error can be raised during commit
* Fix optimistic update checks for composite foreign keys
* Don't raise OptimisticCheckError if db_session is not optimistic
* Handling incorrect datetime values in MySQL
* Improved ImportError exception messages when MySQLdb, pymysql, psycopg2 or psycopg2cffi driver was not found
* desc() function fixed to allow reverse its effect by calling desc(desc(x))
* __contains__ method should check if objects belong to the same db_session
* Fix pony.MODE detection; mod_wsgi detection according to official doc
* A lot of inner fixes
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