title: Add relation related columns to many-to-many table flask-sqlalchemy?
body: <p>I have the following models:</p>
  
  <pre><code>class Page(db.Model):
      id = db.Column(db.Integer, primary_key=True)
      tags = db.relationship('Tag', secondary=tags, lazy='subquery',
          backref=db.backref('pages', lazy=True))
  
  class Tag(db.Model):
      id = db.Column(db.Integer, primary_key=True)
  
  tags = db.Table('tags',
      db.Column('tag_id', db.Integer, db.ForeignKey('tag.id'), primary_key=True),
      db.Column('page_id', db.Integer, db.ForeignKey('page.id'), primary_key=True)
      db.Column('language', db.String(50), nullable=False)
  )
  </code></pre>
  
  <p>Know if I want to make the following additions:</p>
  
  <pre><code>tag = Tag()
  Page.tags.append(tag)
  </code></pre>
  
  <p>How to set the value for the <code>language</code> column for the new added tag. </p>