Re: setattr + unmapped attribute

[Bobby Impollonia]

The behavior here isn't SQLAlchemy-specific. If you change:

class MyClass(Base):

    __tablename__ = 'some_table'

    id = Column(Integer, primary_key=True)

to

class MyClass(object):

    pass

, you will see the same behavior.

On Tuesday, November 13, 2012 5:05:24 PM UTC-8, MikeParent wrote:

With a mapped class instance, if I try and set an unmapped attribute, Sqlalchemy simply adds this new attribute (locally) to the object, and subsequent 'get' operations return the assigned value.

Base = declarative_base()

class MyClass(Base):

__tablename__ = 'some_table'

id = Column(Integer, primary_key=True)

           ...

           obj = MyClass()

           ## This correctly raises 'AttributeError'

           print obj.unmapped_attribute

           ## This does not fail!

           obj.unmapped_attribute = 0

           ## Also does not fail anymore, prints "0"

           print obj.unmapped_attribute 

 

I'd like to have an 'AttributeError thrown whenever I try and set a bad property, similar to the getattr() behavior. Is this possible? Maybe I'm doing something wrong?

(Using SqlAlchemy 0.7.9, Python 2.7)

[MikeParent]

Learn something new every day! Thanks.

[Christopher Galpin]

Found your post with Google seeking the same.

Here is the solution, you handle this with a decorator:

def validate_column_attributes(original):

    def __setattr__(self, key, value):

        if key not in self.__table__.columns:

            raise AttributeError("'%s' has no attribute '%s'" % (self.__table__.name, key))

        return original(self, key, value)

    return __setattr__

Base = declarative_base()

Base.__setattr__ = validate_column_attributes(Base.__setattr__)