Following code and error I am getting:
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 represents 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
__mapper_args__ = {
'polymorphic_identity': 'Node',
'polymorphic_on': type_name,
}
class Property(Node):
"""Class represents a Node providing information about another Node"""
node_id = Column(Integer, ForeignKey('Node.node_id'), primary_key=True)
ref_id = Column(Integer, ForeignKey('Node.node_id'))
__mapper_args__ = {
'polymorphic_identity': 'Property',
}
Error:
sqlalchemy.exc.AmbiguousForeignKeysError: Can't determine join between
'Node' and 'Property'; tables have more than one foreign key constraint
relationship between them. Please specify the 'onclause' of this join
explicitly.
Other classes driving from node don't have this issue, but then they
don't have that second foreign key back to node. Can't figure out how to
sepecify the onclause, since I don't explicitly give the join., and my
searching-foo isn't finding anything on this. I suspect somewhere,
likely in the __mapper_args__ I need to specify the field to join on,
but can't find it.
On a somewhat related note, for purposes of DRY, since all of the
subclasses have the same node_id declaration, and basically the same
__mapper__ is there a way I can add this to Node to push this into the
subclasses? Would I use a @declared_attr, which would need to check if
the type was Node since it is different?
(Background, long time programmer, but somewhat new to python, looking
to learn how with reasons, not just rote recipes to follow)
--
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.
---
You received this message because you are subscribed to the Google Groups
"sqlalchemy" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To view this discussion on the web visit
https://groups.google.com/d/msgid/sqlalchemy/bd6dcf30-f6ee-308d-284f-14aeef4505ae%40Damon-Family.org.
