Hi Michael,
Thank you for your response.
Unfortunately I have already tried to use the __init__ function/catch the
init event but I am only referencing the sub classes in a relationship
which does not seem to actually instantiate classes because the __init__ is
never called/init event is never fired.
Here is a simple version of my models.
class HasSomeAttribute(object):
@declared_attr.cascading
def type(cls):
if has_inherited_table(cls):
if cls.__name__ == 'MySubClass1':
return db.Column(db.Integer, default=1)
else:
return db.Column(db.Integer, default=2)
else:
return db.Column(db.Integer, default=0)
class MyClass(HasSomeAttribute, db.Model):
__tablename__ = 'people4l2'
id = db.Column(db.Integer, primary_key=True)
id1 = db.Column(db.Integer)
id2 = db.Column(db.Integer)
class MySubClass1(MyClass):
pass
class MySubClass2(MyClass):
pass
class Right(db.Model):
id = db.Column(db.Integer, primary_key=True)
subclass_attr = relationship(
'Contact',
secondary= MySubClass1.__table__,
primaryjoin='and_(MySubClass1.type == 802, MySubClass1.id2 ==
Right.id)',
secondaryjoin='and_(MySubClass1.type == 802, MySubClass1.id1 ==
Left.id)'
)
class Left(db.Model):
id = db.Column(db.Integer, primary_key=True)
MyClass is used as a junction table for a bunch of different relationships,
the type field is used to differentiate the relationships.
On Monday, March 30, 2015 at 5:26:30 PM UTC+2, Michael Bayer wrote:
>
>
>
> Pierre B <rocambol...@gmail.com <javascript:>> wrote:
>
> > Hi all,
> >
> > I'm ultimately trying to have different default values for the same
> column. Following the documentation, the @declared_attr.cacading decorator
> seems to be the best approach.
> > Here's my code:
> > class HasSomeAttribute(object):
> > @declared_attr.cascading
> > def type(cls):
> > if has_inherited_table(cls):
> > if cls.__name__ == 'MySubClass1':
> > return db.Column(db.Integer, default=1)
> > else:
> > return db.Column(db.Integer, default=2)
> > else:
> > return db.Column(db.Integer, default=0)
> >
> > class MyClass(HasSomeAttribute, db.Model):
> > __tablename__ = 'people4l2'
> > id = db.Column(db.Integer, primary_key=True)
> >
> > class MySubClass1(MyClass):
> > pass
> >
> > class MySubClass2(MyClass):
> > pass
> >
> > I iterated quite a few times over this but I'm systematically getting
> this error:
> > ArgumentError: Column 'type' on class <class '__main__.MySubClass1'>
> conflicts with existing column 'people4l2.type’
>
> this mapping illustrates MySubClass1 and MySubClass2 as both sharing the
> same table “people4l2”, as they have no __tablename__ attribute, so there
> can only be one “type” column. So in this case it is not appropriate to
> use
> cascading in exactly this way, as MyClass already has a “type” column, and
> that gets attached to the “people4l2” table and that’s it; there can be no
> different “type” column on MySubClass1/MySubClass2.
>
> If you’d like “type” to do something different based on which class is
> being
> instantiated, this is an ORM-level differentiation. Use either the
> constructor __init__() to set it or use the init() event
> (
> http://docs.sqlalchemy.org/en/rel_0_9/orm/events.html?highlight=event%20init#sqlalchemy.orm.events.InstanceEvents.init).
>
>
>
> OTOH if “type” is actually the “polymoprhic discriminator”, which is what
> this looks like, then you’d be looking to just set up “type” as the
> “polymorphic_on” column and set up the “1”, “2”, “0” as the polymorphic
> identity (see
>
> http://docs.sqlalchemy.org/en/rel_0_9/orm/inheritance.html#single-table-inheritance
>
> for a simple example).
>
>
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