[Sqlalchemy-tickets] Issue #4285: session attempted to sort enum.Enum (zzzeek/sqlalchemy)

[moon c. <iss...@bi...>]

New issue 4285: session attempted to sort enum.Enum
https://bitbucket.org/zzzeek/sqlalchemy/issues/4285/session-attempted-to-sort-enumenum

moon cake:

It seems like `_sort_states` in `persistence.py` is trying to sort the primary key(s), irregardless whether it is sortable. In this case, I'm using an `enum.Enum`. Full repro code follows.

```
(sqlalchemy) $ python test.py
Traceback (most recent call last):
  File "test.py", line 35, in <module>
    create_trees(session)
  File "test.py", line 29, in create_trees
    session.query(Tree).merge_result([Tree(color=Color.red), Tree(color=Color.black)])
  File "/tmp/sqlalchemy/lib/python3.6/site-packages/sqlalchemy/orm/session.py", line 572, in __exit__
    self.rollback()
  File "/tmp/sqlalchemy/lib/python3.6/site-packages/sqlalchemy/util/langhelpers.py", line 66, in __exit__
    compat.reraise(exc_type, exc_value, exc_tb)
  File "/tmp/sqlalchemy/lib/python3.6/site-packages/sqlalchemy/util/compat.py", line 187, in reraise
    raise value
  File "/tmp/sqlalchemy/lib/python3.6/site-packages/sqlalchemy/orm/session.py", line 569, in __exit__
    self.commit()
  File "/tmp/sqlalchemy/lib/python3.6/site-packages/sqlalchemy/orm/session.py", line 467, in commit
    self._prepare_impl()
  File "/tmp/sqlalchemy/lib/python3.6/site-packages/sqlalchemy/orm/session.py", line 447, in _prepare_impl
    self.session.flush()
  File "/tmp/sqlalchemy/lib/python3.6/site-packages/sqlalchemy/orm/session.py", line 2254, in flush
    self._flush(objects)
  File "/tmp/sqlalchemy/lib/python3.6/site-packages/sqlalchemy/orm/session.py", line 2380, in _flush
    transaction.rollback(_capture_exception=True)
  File "/tmp/sqlalchemy/lib/python3.6/site-packages/sqlalchemy/util/langhelpers.py", line 66, in __exit__
    compat.reraise(exc_type, exc_value, exc_tb)
  File "/tmp/sqlalchemy/lib/python3.6/site-packages/sqlalchemy/util/compat.py", line 187, in reraise
    raise value
  File "/tmp/sqlalchemy/lib/python3.6/site-packages/sqlalchemy/orm/session.py", line 2344, in _flush
    flush_context.execute()
  File "/tmp/sqlalchemy/lib/python3.6/site-packages/sqlalchemy/orm/unitofwork.py", line 391, in execute
    rec.execute(self)
  File "/tmp/sqlalchemy/lib/python3.6/site-packages/sqlalchemy/orm/unitofwork.py", line 556, in execute
    uow
  File "/tmp/sqlalchemy/lib/python3.6/site-packages/sqlalchemy/orm/persistence.py", line 156, in save_obj
    base_mapper, states, uowtransaction
  File "/tmp/sqlalchemy/lib/python3.6/site-packages/sqlalchemy/orm/persistence.py", line 286, in _organize_states_for_save
    states):
  File "/tmp/sqlalchemy/lib/python3.6/site-packages/sqlalchemy/orm/persistence.py", line 1255, in _connections_for_states
    for state in _sort_states(states):
  File "/tmp/sqlalchemy/lib/python3.6/site-packages/sqlalchemy/orm/persistence.py", line 1277, in _sort_states
    sorted(persistent, key=lambda q: q.key[1])
TypeError: '<' not supported between instances of 'Color' and 'Color'
```

=======

Repro code

```py
import enum
from sqlalchemy import create_engine, Column, Enum
from sqlalchemy.orm import sessionmaker
from sqlalchemy.ext.declarative import declarative_base


class Color(enum.Enum):
    red = 'Red'
    black = 'Black'


Base = declarative_base()


class Tree(Base):
    __tablename__ = 'tree'

    color = Column(Enum(Color), primary_key=True)


engine = create_engine('postgresql://tree:tree@127.0.0.1/trees')
Base.metadata.create_all(engine)

Session = sessionmaker(bind=engine)


def create_trees(session):
    with session.begin_nested():
        session.query(Tree).merge_result([Tree(color=Color.red), Tree(color=Color.black)])

    session.commit()


session = Session()
create_trees(session)
create_trees(session)
```