text: from app import db
  from datetime import datetime
  
  class User(db.Model):
      id = db.Column(db.Integer, primary_key=True)
      username = db.Column(db.String(64), index=True, unique=True)
      email = db.Column(db.String(120), index=True, unique=True)
      password_hash = db.Column(db.String(128))
      books = db.relationship('Book', backref='author', lazy='dynamic')
  
      def __repr__(self):
          return '<User {}>'.format(self.username)
  
  
  class Book(db.Model):
      id = db.Column(db.Integer, primary_key=True)
      title = db.Column(db.String(255))
      author = db.Column(db.String(140))
      genre = db.Column(db.String(56))
      timestamp = db.Column(db.DateTime, index=True, unique=True, default=datetime.utcnow)
      user_id = db.Column(db.Integer, db.ForeignKey('user.id'))
  
      def __repr__(self):
          return 'Book {}>'.format(self.body)
  
      
  