a very basic shop system with sequelize

app.js

const Sequelize = require("sequelize")

////////////////////
// database setup //
////////////////////

var sequelize = new Sequelize('master-thesis', 'root', null, {
  logging: false
})

////////////
// models //
////////////

var User = sequelize.define('User', {
  username: Sequelize.STRING
}, {
  instanceMethods: {
    publishProduct: function(attributes, callback) {
      var self = this

      Product.create(attributes).success(function(product) {
        product.setUser(self).success(function() {
          callback(product)
        })
      })
    },

    addToCart: function(product, callback) {
      var self = this

      this.getCart().success(function(cart) {
        if(cart) {
          cart.addProduct(product).success(callback)
        } else {
          Cart.create().success(function(cart) {
            cart.setUser(self).success(function() {
              cart.addProduct(product).success(function() {
                callback(cart)
              })
            })
          })
        }
      })
    }
  }
})

var Product = sequelize.define('Product', {
  title: Sequelize.STRING
})

var Cart = sequelize.define('Cart', {
  currentValue: Sequelize.FLOAT
})

//////////////////
// associations //
//////////////////

User.hasMany(Product).hasOne(Cart)
Cart.belongsTo(User).hasMany(Product)
Product.belongsTo(User).hasMany(Cart)

///////////
// logic //
///////////

sequelize.sync({ force: true }).success(function() {
  User.create({ username: 'sdepold' }).success(function(sdepold) {
    User.create({ username: 'john doe' }).success(function(johnDoe) {
      sdepold.publishProduct({ title: 'ein produkt' }, function(product) {
        johnDoe.addToCart(product, function(cart) {
          cart.getProducts().success(function(cartItems) {
            console.log(cartItems.map(function(item){ return item.values }))
          })
        })
      })
    })
  })
})