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
--
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