SQLAlchemy - “可选”外键/零对一关系

Question

I am trying to switch from raw SQL to SQLAlchemy and I am struggling modelling a relationship between users and teams. In this situation, a team has a list of users and a user can be in zero or one team .

Somethin like a "optional foreign key" in the table User, referencing to team.id could work, but it would have to be nullable which is not the best manner.

When using raw SQL, I usually create a third table TeamUser(user_id, team_id) with user_id as primary key .

It is entirely possible to replicate this in SQLAlchemy by creating a table, but the python code that need to be written to use those objects becomes less clear.

For example :

add a user to a team :

db.session.add(TeamUser(user_id=user.id, team_id=team.id)) 
#instead of
team.users.append(user)

access the team of a user:

user.team.team (user.team is now the couple (user_id, team_id))

get the list of users as User objects:

map(lambda team_user: team_user.user, team.users)  
#instead of
team.users

So my question is : is there a way to both model this user/team situation and keep an easy syntax while using SQLAlchemy objects?

I have looked at primary join but it doesn't seem to answer this problem. (but maybe I'm wrong)

Answer 1

If you really want to use a join table, take a look at association_proxy .

For a one to many relationship, a foreign key is simpler. The player (user is likely a reserved word) has a reference to a team:

class Player(Base):
    __tablename__ = 'player'
    id = Column(Integer, primary_key=True)
    team_id = Column(Integer, ForeignKey('team.id'))
    team = relationship('Team')

And a team has a list of players:

class Team(Base):
    __tablename__ = 'team'
    id = Column(Integer, primary_key=True)
    players = relationship('Player', back_populates='team')

Then you can add a player via

team.players.append(player) # Player() object

Get a player's team (may be None )

team: Team = player.team

Get the list of players as Player objects

team.players