[Sqlalchemy-tickets] Issue #3801: can't use SQL expression for PK col (zzzeek/sqlalchemy)

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

New issue 3801: can't use SQL expression for PK col
https://bitbucket.org/zzzeek/sqlalchemy/issues/3801/cant-use-sql-expression-for-pk-col

Michael Bayer:


```
#!python

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

Base = declarative_base()


class A(Base):
    __tablename__ = 'a'
    id = Column(Integer, primary_key=True)
    not_pk = Column(Integer)

e = create_engine("sqlite://", echo=True)
Base.metadata.create_all(e)

a1 = A(not_pk=1)
s = Session(e)

s.add(a1)
s.commit()

# works
a1.not_pk = A.not_pk + 1
s.commit()

# fails
a1.id = A.id + 1
s.commit()
```