On Friday, 29 March 2019 13:48:33 UTC, Simon King wrote:
>
>
> You haven't created a relationship() between Vehicle and Dealer, which
> reduces your options a little bit. This should work:
>
> session.query(Vehicle).join(Dealer, Vehicle.supplying_dealer ==
> Dealer.id)
>
> ie. you need to be explicit about the class you are joining to, and
> the join condition. The join condition is necessary because you have 2
> foreign keys between Vehicle and Dealer.
>
> You might want to consider creating relationships between the two
> classes, something like this:
>
> class Vehicle(Base):
> __tablename__ = 'vehicles'
>
> registration = Column(String(10), primary_key=True, nullable=False)
> # note that I've renamed these columns
> supplying_dealer_id = Column(String(64),
> ForeignKey(u'dealers.id'), nullable=False)
> servicing_dealer_id = Column(String(64),
> ForeignKey(u'dealers.id'), nullable=False)
>
> supplying_dealer = relationship(Dealer, supplying_dealer_id ==
> Dealer.id)
> servicing_dealer = relationship(Dealer, servicing_dealer_id ==
> Dealer.id)
>
I'd missed the need to set a relationship in addition to the foreign key.
I've done that and changed Dealer.id to Dealer.dealer_id.
I can't now load any data. It says
"sqlalchemy.exc.NoForeignKeysError: Could not determine join condition
between parent/child tables on relationship Vehicle.supplying_dealer -
there are no foreign keys linking these tables via secondary table
'vehicles.supplying_dealer_id = dealers.dealer_id'. Ensure that
referencing columns are associated with a ForeignKey or
ForeignKeyConstraint, or specify 'primaryjoin' and 'secondaryjoin'
expressions."
It looks OK to me.
The current table definitions are:
class Dealer(Base):
__tablename__ = 'dealers'
dealer_id = Column(String(64), primary_key=True, nullable=False)
name = Column(String(100), nullable=False)
phone_number = Column(String(64), nullable=False)
def __repr__(self):
return "<Dealer(supplying_dealer='%s', registration='%s',
servicing_dealer='%s')>" % (
self.supplying_dealer, self.registration,
self.servicing_dealer)
class Vehicle(Base):
__tablename__ = 'vehicles'
registration = Column(String(10), primary_key=True, nullable=False)
supplying_dealer_id = Column(String(64),
ForeignKey(u'dealers.dealer_id'), nullable=False)
servicing_dealer_id = Column(String(64),
ForeignKey(u'dealers.dealer_id'), nullable=False)
supplying_dealer = relationship(Dealer, supplying_dealer_id ==
Dealer.dealer_id)
servicing_dealer = relationship(Dealer, servicing_dealer_id ==
Dealer.dealer_id)
def __repr__(self):
return "<Vehicle(registration='%s', supplying_dealer='%s',
servicing_dealer='%s')>" % (
self.registration, self.supplying_dealer, self.servicing_dealer)
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http://www.sqlalchemy.org/
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