Don't save CounterField values by default when saving models.
Review Request #9234 - Created Sept. 29, 2017 and submitted
We had a long-standing, hard-to-catch bug where counters would sometimes
end up with incorrect values, requiring a reset of the counters in order
to recompute. This turned out to be due to code
incrementing/decrementing a counter and then another instance somewhere
saving the old counter values back to the database.
The only time a counter's value should be included as part of a standard
save operation is if the value is being reset (saving
None) or if it's
explicitly requested in
While Django does allow for some control over which fields are saved to
the database, there's no way for fields themselves to opt out of saving
a value, which is what we'd prefer. So instead,
a new version of
_do_update()(the model's function that actually
kicks off computing the SQL to update a set of values) that filters out
the values first. This ensures that we never accidentally save a
CounterFieldor any of its subclasses.
Unit tests were added to check on this new behavior.
All Djblets and Review Board unit tests pass.
Manually tested with a solid repro case and saw that the old stale values
were no longer being stored during