code: async function start() {
    // Make sure the database tables are up to date
    await models.sequelize.sync({ force: true });
  
    // Create sample data
    const foo = await models.User.create({ name: 'Foo' });
    const bar = await models.User.create({ name: 'Bar' });
    await foo.createPet({ name: 'Bat' });
    await bar.createPet({ name: 'Baz' });
  
    // Start the GraphQL server
    server.start(() => {
      console.log('Server is running on localhost:4000');
    });
  }
docs: DISCLAIMER: using sequelize#sync is not recommended for production use. Please, please
  use migrations. This method of creating a database is used in this demo for simplicity's sake.