[Sqlalchemy-tickets] Issue #3409: 0.9.x - 1.0.x regression - AttributeError: entity when using label() with attribute of aliased entity (zzzeek/sqlalchemy)

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

New issue 3409: 0.9.x - 1.0.x regression - AttributeError: entity when using label() with attribute of aliased entity
https://bitbucket.org/zzzeek/sqlalchemy/issue/3409/09x-10x-regression-attributeerror-entity

Pavel Brych:

After upgrading to 1.0.2 resp. 1.0.3 SQLAlchemy, this error popped up. It happens when label() is used with attribute of aliased entity.
```
#!python

#!/usr/bin/python
# -*- coding: utf-8 -*-
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import aliased

Base = declarative_base()

class User(Base):
    __tablename__ = 'users'

    id = Column(Integer, primary_key=True)
    username = Column(String(255))
    realname = Column(String(255))

e = create_engine("postgresql://user:passwd@localhost/db_name", echo=True)
Base.metadata.create_all(e)

session = Session(e)

user = aliased(User,name="user")

q = session.query(user.username.label("username"))

print(q.column_descriptions)
```


```
#!python

Traceback (most recent call last):
  File "/home/pavel/python/hores/src/sqlalchemytest.py", line 27, in <module>
    print(q.column_descriptions)
  File "/usr/lib64/python3.4/site-packages/sqlalchemy/orm/query.py", line 2583, in column_descriptions
    for ent in self._entities
  File "/usr/lib64/python3.4/site-packages/sqlalchemy/orm/query.py", line 2583, in <listcomp>
    for ent in self._entities
  File "/usr/lib64/python3.4/site-packages/sqlalchemy/orm/util.py", line 398, in __getattr__
    raise AttributeError(key)
AttributeError: entity
```