old_contents: from app import database
  
  
  class Talk(database.Model):
      id = database.Column(database.Integer, primary_key=True, autoincrement=True)
      title = database.Column(database.String(128), nullable=False)
      description = database.Column(database.String(512))
      speaker_facebook_id = database.Column(database.BIGINT, database.ForeignKey('speaker.facebook_id'),
                                            nullable=False)
  
      liked_by = database.relationship('Liker_Talk', backref='talk', lazy='dynamic')
  
      def __repr__(self):
          return '<Talk %r>' % self.id
  
  
  class Speaker(database.Model):
      facebook_id = database.Column(database.BIGINT, primary_key=True)
      name = database.Column(database.String(128), nullable=False)
  
      talks = database.relationship('Talk', backref='speaker', lazy='dynamic')
  
      def __repr__(self):
          return '<Speaker %r>' % self.facebook_id
  
  
  class Liker_Talk(database.Model):
      liker_facebook_id = database.Column(database.BIGINT, primary_key=True)
      talk_id = database.Column(database.Integer, database.ForeignKey('talk.id'), primary_key=True)
  
      def __repr__(self):
          liker = repr(self.liker_facebook_id)
          talk = repr(self.talk_id)
          return '<Liker_Talk %r>' % ', '.join((liker, talk))
  
new_contents: from app import database
  
  
  class Talk(database.Model):
      id = database.Column(database.Integer, primary_key=True, autoincrement=True)
      title = database.Column(database.String(128), unique=True, nullable=False)
      description = database.Column(database.String(512))
      speaker_facebook_id = database.Column(database.BIGINT, database.ForeignKey('speaker.facebook_id'),
                                            nullable=False)
  
      liked_by = database.relationship('Liker_Talk', backref='talk', lazy='dynamic')
  
      def __repr__(self):
          return '<Talk %r>' % self.id
  
  
  class Speaker(database.Model):
      facebook_id = database.Column(database.BIGINT, primary_key=True)
      name = database.Column(database.String(128), nullable=False)
  
      talks = database.relationship('Talk', backref='speaker', lazy='dynamic')
  
      def __repr__(self):
          return '<Speaker %r>' % self.facebook_id
  
  
  class Liker_Talk(database.Model):
      liker_facebook_id = database.Column(database.BIGINT, primary_key=True)
      talk_id = database.Column(database.Integer, database.ForeignKey('talk.id'), primary_key=True)
  
      def __repr__(self):
          liker = repr(self.liker_facebook_id)
          talk = repr(self.talk_id)
          return '<Liker_Talk %r>' % ', '.join((liker, talk))
  
subject: Make title unique Talk property