Models

from flask_sqlalchemy import SQLAlchemy
from sqlalchemy import ForeignKey
from sqlalchemy.orm import relationship
from datetime import datetime, timedelta
from app import db, bcrypt
import uuid

class User(db.Model):
    __tablename__ = 'user'
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(80), unique=True)
    email = db.Column(db.String(120), unique=True)
    password = db.Column(db.String(255))
    admin = db.Column(db.Boolean(), default=False)
    articles = db.relationship('Article', backref='user', lazy='dynamic')
    messages = db.relationship('Message', backref='user', lazy='dynamic')
    timestamp = db.Column(db.DateTime)
    changepasswordrequest = db.relationship('ChangePasswordRequest', uselist=False, backref='user')
    emailverification = db.relationship('EmailVerification', uselist=False, backref='user')

    def __init__(self, username, email, password, timestamp=None):
        self.username = username
        self.email = email
        self.password = bcrypt.generate_password_hash(password)
        self.timestamp = datetime.utcnow()

    def __repr__(self):
        return '<User %r>' % self.username

class Message(db.Model):
    __tablename__ = 'message'
    id = db.Column(db.Integer, primary_key=True)
    title = db.Column(db.String(50))
    body = db.Column(db.String())

    to_id = db.Column(db.Integer, ForeignKey("user.id"))
    from_id = db.Column(db.Integer, ForeignKey("user.id"))

    from_user = db.relationship("User", foreign_keys=[to_id])
    to_user = db.relationship("User", foreign_keys=[from_id])

    def __init__(self, title, body, to_user, from_user):
        self.title = title
        self.body = body
        self.to_user = to_user
        self.from_user = from_user

    def __repr__(self):
        return '<Message %r>' % self.id

# My error is
# sqlalchemy.exc.AmbiguousForeignKeysError
AmbiguousForeignKeysError: Could not determine join condition between parent/child tables on relationship User.messages - there are multiple foreign key paths linking the tables.  Specify the 'foreign_keys' argument, providing a list of those columns which should be counted as containing a foreign key reference to the parent table.