[Sqlalchemy-tickets] Issue #3469: comparison in persistence.py can trip up on clauseelement sitautions (zzzeek/sqlalchemy)

[Mike B. <iss...@bi...>]

New issue 3469: comparison in persistence.py can trip up on clauseelement sitautions
https://bitbucket.org/zzzeek/sqlalchemy/issue/3469/comparison-in-persistencepy-can-trip-up-on

Mike Bayer:

We're seeing stack traces like this:


```
#!

 File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/session.py", line 2122, in _flush
    transaction.rollback(_capture_exception=True)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/util/langhelpers.py", line 60, in __exit__
    compat.reraise(exc_type, exc_value, exc_tb)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/session.py", line 2086, in _flush
    flush_context.execute()
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/unitofwork.py", line 373, in execute
    rec.execute(self)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/unitofwork.py", line 532, in execute
    uow
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/persistence.py", line 170, in save_obj
    mapper, table, update)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/persistence.py", line 630, in _emit_update_statements
    lambda rec: (
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/persistence.py", line 459, in _collect_update_commands
    value, state.committed_state[propkey]):
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/sql/elements.py", line 2726, in __bool__
    raise TypeError("Boolean value of this clause is not defined")
TypeError: Boolean value of this clause is not defined
```

examples include numpy objects as well as geoalchemy2 objects:


```
#!python

import geoalchemy2
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base


Base = declarative_base()


class A(Base):
    __tablename__ = 'tests'
    id = Column(Integer, primary_key=True)
    geom = Column(geoalchemy2.Geometry('POLYGON'))


e = create_engine("postgresql://scott:tiger@localhost/test", echo=True)
Base.metadata.create_all(e)

s = Session(e)
s.add(A(id=1, geom='POLYGON((0 0,1 0,1 1,0 1,0 0))'))
s.commit()
a1 = s.query(A).first()
a1.geom = None

s.commit()

```

in 0.9 we use attributes.from_scalar_attribute() which does the is_equals() and then compares it to "is True", so that's why we're suddenly failing.