Self-referential database with extra fields in sqlalchemy

Question

I want to write a self-referential database structure for my messaging system using Flask and SQLAlchemy. Tables are very simple:

class User(db.Model):
    __tablename__ = 'user'
    id = Column(Integer, primary_key=True)
    messages = db.relationship(...)

    def addMessage (self, friend, message):
       ...
       self.messages.append(friend)
       return self

and message table is:

class Message (db.Model):
    __tablename__ = 'message'

    id = db.Column(db.Integer, primary_key=True)
    emmiter_id = db.Column(db.Integer, db.ForeignKey('user.id'))
    receiver_id = db.Column(db.Integer, db.ForeignKey('user.id'))
    text = db.Column(db.Text)

I want to know how will the relationship with my user table look like? and how can I insert data on the message table?

This is what I wrote in user table as relationship, but it is not working:

messages = db.relationship('User',
    secondary = Message,
    primaryjoin = (Message.emmiter_id == id),
    secondaryjoin = (Message.receiver_id == id),
    backref = db.backref('correspondence', lazy = 'dynamic'),
    lazy = 'dynamic')

Answer 1

After working a lot around this problem I found the solution with primaryjoin between user table and message table. Here is the working code

# Messaging system table
class Message(db.Model):
    __tablename__ = 'message'

    emmiter_id = db.Column(db.Integer, db.ForeignKey('user.id'), primary_key=True)
    recipient_id = db.Column(db.Integer, db.ForeignKey('user.id'), primary_key=True)
    text = db.Column(db.Text, nullable=False)

and user table like :

class User (db.Model):
    __tablename__ = 'user'

    id = db.Column(db.Integer, primary_key=True)
    inbox = db.relationship('Message',backref='sender', primaryjoin=id==Message.emmiter_id)
    outbox = db.relationship('Message',backref='receiver', primaryjoin=id==Message.recipient_id)

and here is how you can add a message in message table:

message = Message(text="dsf", sender=sender , receiver=receiver)