Why am I getting AmbiguousForeignKeysError?

Question

I\'ve run into an issue after following the SqlAlchemy guide here.

Given the following simplified module:

class _Base():
    id_ = Column(Integer, primary_         


        

Answer 1

The issue is with the definition of this relationship match = relationship("MatchResult") for the Player class. If you completely remove this line, and use the below definitions for the relationships, all the queries you mentioned should work as expected:

class Player(Base, BlgMixin):
    __tablename__ = "player"

    name_ = Column(String(100))


class MatchResult(Base, BlgMixin):
    __tablename__ = "match_result"

    p1_id = Column(ForeignKey(Player.id_))
    p2_id = Column(ForeignKey(Player.id_))

    p1 = relationship(Player, foreign_keys=p1_id)
    p2 = relationship(Player, foreign_keys=p2_id)

In fact, the desired select query can also be constructed, but you need to specify the relationships explicitly on JOINs:

player_1 = aliased(Player)
player_2 = aliased(Player)
q = (
    dal.session
    .query(
        MatchResult.p1_id,
        player_1.name_,
        MatchResult.p2_id,
        player_2.name_,
    )
    .join(player_1, MatchResult.p1)  # explicitly specify which relationship/FK to join on
    .join(player_2, MatchResult.p2)  # explicitly specify which relationship/FK to join on
)

---

I would, however, make few more changes to the model to make it even more user-friednly:

1. add backref to the relationship so that it can be navigated back from the Player
2. add a property to show all the matches of one player for both sides

Model definitions:

class Player(Base, BlgMixin):
    __tablename__ = "player"

    name_ = Column(String(100))

    @property
    def all_matches(self):
        return self.matches_home + self.matches_away


class MatchResult(Base, BlgMixin):
    __tablename__ = "match_result"

    p1_id = Column(ForeignKey(Player.id_))
    p2_id = Column(ForeignKey(Player.id_))
    
    p1 = relationship(Player, foreign_keys=p1_id, backref="matches_home")
    p2 = relationship(Player, foreign_keys=p2_id, backref="matches_away")

This will allow navigating the relationships as per below example:

p1 = session.query(Player).get(1)
print(p1)
for match in p1.all_matches:
    print(" ", match)