Declaring functional (func.lower) does not work as expected with declarative

[Former user]

Attached is a very simple case.

[Former user]

Err, declaring functional index does not work.

[Mike Bayer]

the index needs to be associated with at least one column in the table. The string "tag" is not a column, to SQLAlchemy its an arbitrary expression. usage is as follows:

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

Base = declarative_base()


class FuncIndex(Base):
    __tablename__ = 'funcindex'

    id = Column(Integer, primary_key=True)
    tag = Column(String(20))
    __table_args__ = (
        Index('funcindex_idx', func.lower(tag)),
    )

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