endorsement/models.py

from app import db

endorsed = db.Table('endorses',
    db.Column('user_id', db.String, db.ForeignKey('user.username'), primary_key=True),
    db.Column('achievement_id', db.Integer, db.ForeignKey('achievement.id'), primary_key=True)
)

class User(db.Model):
    username = db.Column(db.String(80), unique=True, nullable=False, primary_key=True)

    def to_obj(self):
        return {
            "username": self.username,
            "achievements": [x.to_obj() for x in Achievement.query.filter_by(achieved_by=self.username).all()]
        }

    def __repr__(self):
        return '<User %r>' % self.username
    
    # For login
    def is_authenticated(self):
        return True

    def is_active(self):
        return True

    def is_admin(self):
        return self.admin

    def is_anonymous(self):
        return False

    def get_id(self):
        return str(self.username)

class Achievement(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(128), nullable=False)
    achieved_by = db.Column(db.Integer, db.ForeignKey("user.username"), nullable=False)

    endorsed_by = db.relationship('User', secondary=endorsed, lazy='subquery', backref=db.backref('user', lazy=True))

    def to_obj(self):
        return {
            "id": self.id,
            "name": self.name,
            "endorsed_by": [x.username for x in self.endorsed_by], # Don't show full user object to avoid infinite loops
        }

    def __repr__(self):
        return '<Achievement %r from %r>' % (self.name, self.achieved_by.name)