orm.Query() constructor (used w/ undocumented behavior) raising "Boolean value of this clause is not defined" exception

Migrated issue, originally created by Patrick Rusk

(This problem was noted in comments in https://github.com/zzzeek/sqlalchemy/commit/3fa38a1a2313b4644daa431d629394d6bb14497a but not followed up on.)

The sqlalchemy.orm.Query() class takes an entities parameter defined to be “a sequence of entities and/or SQL expressions”, but it used to actual accept a single SQL expression as well. Now, some such expressions cause a “TypeError: Boolean value of this clause is not defined” exception to be raised.

The offending line is https://github.com/zzzeek/sqlalchemy/blob/master/lib/sqlalchemy/orm/query.py#L150

As noted in the comments, changing it to if entities is not None: would probably fix the issue.

Test case:

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer
import sqlalchemy.sql

class User(declarative_base()):
    __tablename__ = 'users'
    id = sqlalchemy.Column(sqlalchemy.Integer, primary_key=True)

select = sqlalchemy.sql.func.max(User.id).label('max')
query = sqlalchemy.orm.Query(select)

…works under 1.2.7, but generates this stack trace under 1.2.8…

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-1-cf50a8343d19> in <module>()
      8 
      9 select = sqlalchemy.sql.func.max(User.id).label('max')
---> 10 query = sqlalchemy.orm.Query(select)

/Users/patrick/.virtualenvs/shackleton/lib/python2.7/site-packages/sqlalchemy/orm/query.pyc in __init__(self, entities, session)
    140         self.session = session
    141         self._polymorphic_adapters = {}
--> 142         self._set_entities(entities)
    143 
    144     def _set_entities(self, entities, entity_wrapper=None):

/Users/patrick/.virtualenvs/shackleton/lib/python2.7/site-packages/sqlalchemy/orm/query.pyc in _set_entities(self, entities, entity_wrapper)
    148         self._primary_entity = None
    149         self._has_mapper_entities = False
--> 150         if entities:
    151             for ent in util.to_list(entities):
    152                 entity_wrapper(self, ent)

/Users/patrick/.virtualenvs/shackleton/lib/python2.7/site-packages/sqlalchemy/sql/elements.pyc in __bool__(self)
    485 
    486     def __bool__(self):
--> 487         raise TypeError("Boolean value of this clause is not defined")
    488 
    489     __nonzero__ = __bool__

TypeError: Boolean value of this clause is not defined

Anyone experiencing this can easily fix their issue by throwing [] around their expression, but it is a breaking change (of an undocumented feature).

(Please forgive the nonsensical test case above. I’ve never used SQLAlchemy. Just diagnosing a bug in someone else’s code.)

[sqlalchemy-bot]

Patrick Rusk wrote:

Michael, I don’t disagree with any of your analysis, and I think my original description pretty much laid out the same. Good change to the title. I’ll merely note a couple things.

1. It is arguably more pythonic to allow one expression to be passed in by itself, rather than requiring that it be wrapped in a sequence. I don’t feel strongly about such things, nor do I know enough about SQLAlchemy to know if that fits in with the feel of the library. But a case could be made to support it and change the documentation (since it has effectively been supported up until now).

2. If you decide that behavior should explicitly not be allowed, I would recommend not changing it in a patch release, but adding deprecation warnings to the next few release notes and changing it in a major release that explicitly removes deprecated functionality (even undocumented).

Thanks for your attention. I appreciate it.

[sqlalchemy-bot]

Changes by Michael Bayer (@zzzeek):

• changed status to closed