you might be able to use the declared_attr __mapper__ but you would need to
omit that erroneous inherit condition if the class is "Name". IMO it would be
easier to follow and understand by simply using explicit __mapper_args__ on
each class but this depends on what you're doing.
On Thu, Sep 3, 2020, at 7:24 AM, Richard Damon wrote:
> I've tried taking my code and changing the ForeignKey to be to Node, and
> that doesn't change the Warning.
> Is the problem trying to DRY with the @declared_attr __mapper__?
>
> On 9/2/20 11:29 PM, Mike Bayer wrote:
> > well you are giving Name an inherit condition that conflicts with how
> > you set up the foreign key.
> >
> > Name.node_id FKs to Property.node_id
> >
> > but then inherit condition is Name.node_id -> Node.node_id
> >
> > There seems to be a little unsmoothness to actually being able to
> > configure it that way, that is, skipping over Property.node_id, but in
> > this case your FKs make it clear what you're going for which is the
> > "normal' setup of Name->Property->Node so you can remove "inherit
> > condition" from Name and it works fine:
> >
> > class Name(Property):
> > __tablename__ = 'Name'
> >
> > node_id = Column(Integer, ForeignKey("Property.node_id"),
> > primary_key=True)
> >
> > __mapper_args__ = {
> > "polymorphic_identity": "Name",
> > }
> >
> >
> > or set it:
> >
> > class Name(Property):
> > __tablename__ = 'Name'
> >
> > node_id = Column(Integer, ForeignKey("Property.node_id"),
> > primary_key=True)
> >
> > __mapper_args__ = {
> > "polymorphic_identity": "Name",
> > "inherit_condition": node_id == Property.node_id,
> > }
> >
> >
> >
> > On Wed, Sep 2, 2020, at 10:08 PM, Richard Damon wrote:
> >> Here is the code, note in all cases node_id are foreign key/primary_key
> >> to a primary_key down the chain:
> >>
> >>
> >> class Base:
> >> """Base Class for SQLAlchemy ORM Classes"""
> >> @declared_attr
> >> def __tablename__(cls):
> >> """Default the Table Name to the Class Name"""
> >> return cls.__name__
> >>
> >> Base = declarative_base(cls=Base)
> >>
> >> class Node(Base):
> >> """Class repesents the base of the User Data types."""
> >> node_id = Column(Integer, primary_key=True)
> >> type_name = Column(String(255), nullable=False) # todo should come
> >> from type_id
> >>
> >> @declared_attr
> >> def __mapper_args__(cls):
> >> if cls.__name__ == 'Node' :
> >> __mapper_args__ = {
> >> 'polymorphic_identity': 'Node',
> >> 'polymorphic_on': cls.type_name,
> >> }
> >> else:
> >> __mapper_args__ = {
> >> 'polymorphic_identity': cls.__tablename__,
> >> "inherit_condition": cls.node_id == Node.node_id
> >> }
> >> return __mapper_args__
> >>
> >> class Property(Node):
> >> node_id = Column(Integer, ForeignKey('Node.node_id'),
> >> primary_key=True)
> >> ref_id = Column(Integer, ForeignKey('Node.node_id'))
> >>
> >> class Name(Property):
> >> node_id = Column(Integer, ForeignKey('Property.node_id'),
> >> primary_key=True)
> >>
> >>
> >> On 9/2/20 9:39 PM, Mike Bayer wrote:
> >> > there's an FAQ entry, a little bit dated but the general idea is still
> >> > there, at:
> >> >
> >> > https://docs.sqlalchemy.org/en/13/faq/ormconfiguration.html#i-m-getting-a-warning-or-error-about-implicitly-combining-column-x-under-attribute-y
> >> >
> >> > for joined table inheritance, where Name(Node) -> node_id are FK ->
> >> > PK, the warning isn't emitted. so please share the mapping if it is
> >> > doing this when it shouldnt.
> >> >
> >> >
> >> > On Wed, Sep 2, 2020, at 9:08 PM, Richard Damon wrote:
> >> >> I am getting the following error:
> >> >>
> >> >> SAWarning: Implicitly combining column Node.node_id with column
> >> >> Name.node_id under attribute 'node_id'. Please configure one or more
> >> >> attributes for these same-named columns explicitly.
> >> >>
> >> >> In my case I am using poymorphic classes by joining with the ORM. Node
> >> >> is the base of the hierarchy (derived from declarative_base), then I
> >> >> have a class Property derived from it, and a class Name derived from
> >> >> Property. Each class has a primary_key named node_id, with a
> >> foreign key
> >> >> constraint one step done the hierarchy. I have also tried making
> >> all the
> >> >> Foreign key constraints point to Node.node_id and it doesn't make a
> >> >> difference.
> >> >>
> >> >> It is just a warning, and the lookup does seem to make the double
> >> join,
> >> >> so it doesn't seem to be a big problem, but it seems it want me to
> >> >> configure something for these, but I am not sure what.
> >> >>
> >> >> Two level inheritance is working just fine, it is just where it
> >> hits the
> >> >> 3rd level that it seems to want something explicit.
> >> >>
> >> >> --
> >> >> Richard Damon
> >>
> >>
> >> --
> >> Richard Damon
>
> --
> Richard Damon
>
> --
> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
> http://www.sqlalchemy.org/
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--
SQLAlchemy -
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http://www.sqlalchemy.org/
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