I can't seem to construct a relationship against this ServiceInstance class
without having
the Endpoint class inherit from a new declarative_base(). I've tried
several different
methods of calling relationship() and the error messages are fairly
similar. Below I've
shown the two classes as well as the various relationship() calls and the
resulting
errors. I'm new to SQLAlchemy so apologies if I'm overlooking something
very basic, but I
don't understand the errors given that I have service_id = Column(
ForeignKey(ServiceInstance.service_id), primary_key=True)
class Endpoint(Base):
__tablename__ = 'endpoints'
__table_args__ = {'schema': 'nms'}
service_id = Column(ForeignKey(ServiceInstance.service_id),
primary_key=True)
endpoint_type = Column(Enum('Service', 'Address'))
service_instance = relationship(
ServiceInstance,
foreign_keys=service_id,
backref=backref('endpoints', cascade='all, delete-orphan'))
class ServiceInstance(Base):
__tablename__ = 'services'
__table_args__ = (
{'schema': 'customer_inquiry'}
)
service_id = Column(Integer, primary_key=True)
service_instance_id = Column(String(12), unique=True)
title = Column(String(255))
definition_title = Column(String(255), nullable=False)
description = Column(Text)
category = Column(ForeignKey(ServiceCategory.category), nullable=False)
price = Column(Numeric, CheckConstraint('price >= 0'), nullable=False)
units_included = Column(
Numeric,
CheckConstraint('units_included IS NULL OR units_included >=
0'))
unit_price = Column(
Numeric,
CheckConstraint('unit_price IS NULL OR unit_price >= 0'))
sqlalchemy.exc.NoForeignKeysError: Could not determine join condition
between parent/child
tables on relationship Endpoint.service_instance - there are no foreign
keys linking these
tables. Ensure that referencing columns are associated with a ForeignKey
or
ForeignKeyConstraint, or specify a 'primaryjoin' expression.
service_instance = relationship(
ServiceInstance,
primaryjoin=service_id == ServiceInstance.service_id,
backref=backref('endpoints', cascade='all, delete-orphan'))
sqlalchemy.exc.ArgumentError: Could not locate any simple equality
expressions involving
locally mapped foreign key columns for primary join condition
'nms.endpoints.service_id =
customer_inquiry.services.service_id' on relationship
Endpoint.service_instance.
Ensure that referencing columns are associated with a ForeignKey or
ForeignKeyConstraint,
or are annotated in the join condition with the foreign() annotation. To
allow comparison
operators other than '==', the relationship can be marked as viewonly=True.
service_instance = relationship(
ServiceInstance,
primaryjoin=service_id == ServiceInstance.service_id,
viewonly=True,
backref=backref('endpoints', cascade='all, delete-orphan'))
sqlalchemy.exc.ArgumentError: Can't determine relationship direction for
relationship
'Endpoint.service_instance' - foreign key columns are present in neither
the parent nor
the child's mapped tables
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