相同型号中的烧瓶-sqlalchemy 一对一和多对一

Question

I'm trying to make an invitation system where one User has an InvitationToken that can be sent to multiple invitees . Each User can have only one token (one-to-one), as well as be an invitee in multiple tokens (many-to-one).

This is what I have so far:

InvitationToken.py

class InvitationToken(db.Model, SerializeMixin, TimestampMixin):
    __tablename__ = "invitation_token"

    """
    The relationship to the User model. An InvitationToken can have many Users as invitees.
    """
    invitees = db.relationship(
        "User", back_populates="invitee_token", foreign_keys="User.invitee_token_id"
    )

    """
    The relationship to the User model. An InvitationToken can have only one User.
    """
    user_id = db.Column(UUID(as_uuid=True), db.ForeignKey("app_user.id"), index=True)
    user = db.relationship(
        "User",
        back_populates="invitation_token",
        foreign_keys=[user_id],
        uselist=False,
    )

User.py

class User(db.Model, TimestampMixin):
    __tablename__ = "app_user"

    """
    The relationship to the InvitationToken model. A User can have only one InvitationToken.
    """
    invitation_token_id = db.Column(
        UUID(as_uuid=True), db.ForeignKey("invitation_token.id"), index=True
    )
    invitation_token = db.relationship(
        "InvitationToken",
        back_populates="user",
        cascade="delete",
        foreign_keys=[invitation_token_id],
        uselist=False,
    )

    """
    The relationship to the InvitationToken model. A User can have only one InvitationToken as invitee.
    """
    invitee_token_id = db.Column(
        UUID(as_uuid=True), db.ForeignKey("invitation_token.id"), index=True
    )
    invitee_token = db.relationship(
        "InvitationToken",
        back_populates="invitees",
        foreign_keys=[invitee_token_id],
    )

I'm getting the following error with my current configuration:

sqlalchemy.exc.ArgumentError: InvitationToken.user and back-reference User.invitation_token are both of the same direction symbol('MANYTOONE').  Did you mean to set remote_side on the many-to-one side ?

What am I missing?

Answer 1

I found a solution, although I do not fully understand it. But it works:

class InvitationToken(db.Model, SerializeMixin, TimestampMixin):
    __tablename__ = "invitation_token"

    """
    The relationship to the User model. An InvitationToken can have many Users as invitees.
    """
    invitees = db.relationship(
        "User",
        back_populates="invitee_token",
        foreign_keys="User.invitee_token_id",  # Changed this
    )

    """
    The relationship to the User model. An InvitationToken can have only one User.
    """
    user_id = db.Column(UUID(as_uuid=True), db.ForeignKey("app_user.id"), index=True)
    user = db.relationship(
        "User",
        back_populates="invitation_token",
        foreign_keys="User.invitation_token_id",  # Changed this
        uselist=False,
    )

User was left unchanged. This got rid of the error and allowed me to run Flask and have the models behave how I wanted.