使用SqlAlchemy的连接条件错误

Question

I'm trying to use SQLAlchemy on my python app but I have a problem with the many to many relationship. I have 4 tables:

users, flags, commandes, channels, and commandes_channels_flags

commandes_channels_flags contain a foreign key for each concerned table (commandes, channels and flags)

An user has a flag_id as foreign key too.

So I try to link commandes, channels and flag. the objective is to know that a command can run on a channel for a flag.

I did this:

from sqlalchemy import Column, Integer, String, ForeignKey
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship

Base = declarative_base()


class User(Base):
    __tablename__ = 'users'

    id = Column(Integer, primary_key=True)
    pseudo = Column(String(50), unique=True, nullable=False)
    flag_id = Column(ForeignKey('flags.id'))


class Flag(Base):
    __tablename__ = 'flags'

    id = Column(Integer, primary_key=True)
    irc_flag = Column(Integer)
    nom = Column(String(50))

    users = relationship("User", backref="flag", order_by="Flag.irc_flag")
    commande = relationship("Commande", secondary="commandes_channels_flags", back_populates="flags")
    channel = relationship("Channel", secondary="commandes_channels_flags", back_populates="flags")


class Channel(Base):
    __tablename__ = 'channels'

    id = Column(Integer, primary_key=True)
    uri = Column(String(50))
    topic = Column(String(255))

    commande = relationship("Commande", secondary="commandes_channels_flags", back_populates="channels")
    flag = relationship("Flag", secondary="commandes_channels_flags", back_populates="channels")


class Commande(Base):
    __tablename__ = 'commandes'

    id = Column(Integer, primary_key=True)
    pattern = Column(String(50))

    channel = relationship("Channel", secondary="commandes_channels_flags", back_populates="commandes")
    flag = relationship("Flag", secondary="commandes_channels_flags", back_populates="commandes")


class CommandeChannelFlag(Base):
    __tablename__ = 'commandes_channels_flags'

    id = Column(Integer, primary_key=True)
    commande_id = Column(ForeignKey('commandes.id'))
    channel_id = Column(ForeignKey('channels.id'))
    flag_id = Column(ForeignKey('flags.id'))

But I have this error:

sqlalchemy.exc.InvalidRequestError: Mapper 'Mapper|Commande|commandes' has no property 'channels'

I understand that I have an error in my tables linking but I can't find it.

Answer 1

back_populates needs to match the exact name of the related property on the other model. In Channel , you have back_populates="channels" , but in Commande , you have:

channel = relationship("Channel", secondary="commandes_channels_flags", back_populates="commandes")

Instead, change channel = relationship to channels = relationship .

You'll also need to change the other relationship properties to Flag.commandes , Flag.channels , Channel.commandes , Channel.flags , and Commande.flags to match your back_populates arguments.