title: Flask foreign_keys still shows AmbiguousForeignKeysError
body: <p>I have two foreign keys in an entity refering to another entity.
  Here is how it looks</p>
  
  <pre><code>    class Review(db.Model):
        __tablename__ = 'Review'
        id = db.Column(db.Integer, primary_key = True)
        user_id = db.Column(db.Integer, db.ForeignKey('User.id'), nullable=False)
        business_user_id = db.Column(db.Integer, db.ForeignKey('User.id'), nullable=False)
        user = db.relationship('User', foreign_keys=[user_id])
        business_user = db.relationship('User', foreign_keys=[business_user_id])
  </code></pre>
  
  <p>and </p>
  
  <pre><code>class User(db.Model):
    __tablename__ = 'User'
    id = db.Column(db.Integer, primary_key = True)
    reviews = db.relationship('Review', backref='user',
                              lazy='dynamic')
  </code></pre>
  
  <p>However, it still shows me an error saying </p>
  
  <blockquote>
    <p>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</p>
  </blockquote>
  
  <p>The above workaround is what I get from some other posts. I have checked and changed many times, and still no luck. I wonder if it's already correct or there is something I miss. Need help</p>