On Nov 10, 2011, at 12:57 PM, Michael Bayer wrote:
>
> On Nov 10, 2011, at 9:34 AM, Mark Erbaugh wrote:
>
>> I'm trying to use data from a sequence to add columns to a SQLAlchemy table
>> created declaratively. Here's what I'm doing:
>>
>> class Sizing(Base):
>> __tablename__ = 'sizing'
>> id = Column(Integer, primary_key=True)
>>
>> [...]
>>
>>
>> for name in ('column1', 'column2', 'column3', ...):
>> x = Column(type_=Integer)
>> x.name = name
>> Sizing.__table__.append_column(x)
>
>
> that will just add the column to the table but won't map it. the mapper
> isn't aware of this operation.
>
>>
>> This works as far as creating the table in the database, i.e. viewing the
>> database shows columns named column1, column2, column3, etc, but code like
>> getattr(sizing, 'column1') (sizing is an instance of Sizing) is failinging
>> with a message "'Sizing' object has no attribute 'column1'"
>>
>> While code like:
>>
>> Sizing.colum1 = Column(Integer)
>>
>> works, but
>
> right so that hits the __setattr__ of the DeclarativeMeta class which
> receives the Column object, checks it out, and assigns it correctly to the
> mapper and table.
>
>>
>> Sizing.__dict__['column1'] = Column(Integer)
>
> In general, you should never set attributes this way from the outside, that's
> just a Python thing, as you're bypassing whatever attribute set mechanics may
> be present on the target object.
>
>> or
>>
>> Sizing.__setattr__(Sizing, 'column1', Column(Integer))
>
> this is not much different as again you're bypassing instrumentation that may
> be available on the class. Use the Python setattr() function instead:
> setattr(Sizing, "name", object).
Thanks so much!
Mark
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