How to override a column name in sqlalchemy using reflection and descriptive syntax

Question

Hello I\'m trying to port a legacy application to python with sqlalchemy.

The application\'s existing database has about 300 tables and in every table there is a col

Answer 1

You can have your cake and eat it too. Define the columns you want to rename; sqlalchemy will automatically infer any columns you don't mention.

>>> from sqlalchemy import *
>>> from sqlalchemy.ext.declarative import declarative_base
>>> 
>>> engine = create_engine("sqlite:///:memory:")
>>> 
>>> engine.execute("""
... create table accnt (
...     id integer primary key,
...     code varchar(20),
...     def varchar(50)
... )
... """)

>>> 
>>> Base = declarative_base()
>>> 
>>> Base.metadata.bind = engine
>>> 
>>> class Accnt(Base):
...     __tablename__ = 'accnt'
...     __table_args__ = {'autoload': True}
...     def_ = Column('def', String)
... 
>>> Accnt.def_

>>> Accnt.code

>>> 

EDIT:

By supplying a __table__ argument, you're telling the declarative extension that you already have a properly configured Table that you'd like to use. But that's not true; you want to have the def column referred to by another name in the class. By using __tablename__ and __table_args__, you defer the construction of the table until after you've told declarative how you want to use that table. There's no elegant work-around if you are dead set on using __table__. You can provide a property that aliases the column or you may be able to specify the column as _def = getattr(__table__.c, 'def').

Really, you should just use __tablename__; It's both more convenient and more flexible, and this is a great example of why.

(as an aside, it's most conventional to give alternate identifiers a trailing underscore instead of a leading underscore, use def_ instead of _def; leading underscores usually signify that the name is 'private' or 'an implementation detail', if the name is meant to be public, but looks like a private name, it may cause more confusion than is necessary)