I have tried calling relationship without foreign_keys or primaryjoin, in
which case I get an error message suggesting I specify foreign_keys. Base
is the same class for both model classes in the case where this does not
work. When each model class has a different Base class things work fine.
Also it is a 1-to-1 relationship, I just missed that s in the backref.
On Thursday, June 12, 2014 12:03:29 PM UTC-4, Simon King wrote:
>
> On Thu, Jun 12, 2014 at 4:39 PM, <ty...@beanfield.com <javascript:>>
> wrote:
> > 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
> >
>
> With those column definitions, this should Just Work - you shouldn't
> need foreign_keys or primaryjoin parameters in the relationship
> definition, since there is only 1 foreign key and no ambiguity.
>
> (I'm slightly confused by your columns though - is service_id really
> the only primary key of Endpoint? In which case, this would have to be
> a 1-to-1 relationship, but your "endpoints" backref implies that you
> expect there to be more than one endpoint per service)
>
> Did you say that "Base" is the same class in both cases? Foreign key
> relationships are looked up in the Metadata instance which is attached
> to the declarative_base class, so if you have 2 different Base
> classes, SA won't be able to resolve the foreign keys. You can work
> around this by getting the 2 Base classes to share the same Metadata
> instance:
>
>
> http://docs.sqlalchemy.org/en/rel_0_9/orm/extensions/declarative.html#accessing-the-metadata
>
>
> Hope that helps,
>
> Simon
>
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