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
>>
>> --
>> 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 description.
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>>
>
> --
> 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
> description.
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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 description.
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