yup that was the idea
On Thu, Sep 3, 2020, at 10:24 AM, Richard Damon wrote:
> I have a large number (around a dozen or more, and likely to grow) of
> derived classes, so I was hoping to cut down repetition with the
> @declared_attr.
> So, 3rd (or farther) derived classes need the inherit_condition to point
> to their immediate base. That does seem to remove the warning.
>
> On 9/3/20 9:58 AM, Mike Bayer wrote:
> > 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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> >>
> >
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> > The Python SQL Toolkit and Object Relational Mapper
> >
> > http://www.sqlalchemy.org/
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> --
> Richard Damon
>
> --
> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
> http://www.sqlalchemy.org/
>
> To post example code, please provide an MCVE: Minimal, Complete, and
> Verifiable Example. See http://stackoverflow.com/help/mcve for a full
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http://www.sqlalchemy.org/
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