[Sqlalchemy-tickets] Issue #3476: StaleDataError in sqlalchemy 1.0.6 (zzzeek/sqlalchemy)

[Patrick H. <iss...@bi...>]

New issue 3476: StaleDataError in sqlalchemy 1.0.6
https://bitbucket.org/zzzeek/sqlalchemy/issues/3476/staledataerror-in-sqlalchemy-106

Patrick Hayes:

When calling `bulk_update_mappings` in version 1.0.6, occasionally StaleDataErrors emerge.

Previously I was using the fork at https://github.com/pfhayes/sqlalchemy (from this GitHub PR: https://github.com/zzzeek/sqlalchemy/pull/181) and no StaleDataErrors were ever observed.

I tried updating to 1.0.6 and StaleDataErrors started to occur frequently. They happen intermittently when calling code like this:

```python
Base = declarative_base()
class User(Base):
  id = Column(BigInteger, primary_key=True)
  score = Column(DOUBLE_PRECISION)

session.bulk_update_mappings(User, {
  'id': X, 'score': Y,
  ...
})
```

The StaleDataError typically looks like 

```
StaleDataError: UPDATE statement on table 'users' expected to update 18 row(s); 17 were matched.
```

It seems to always expect n+1 when n are matched.

I haven't been able to get a consistent repro. Any suggestions on this?

Responsible: zzzeek