An explanation of how to define a One-to-One relationship in Sequelize and different ways of create the linked objects

sequelize-belongs-to-example.js

// Product Model definition, called 'product' and associated with table 'products'
var Product = this.sequelize.define('product', {
  title: Sequelize.STRING
});

// User Model definition, called 'user' and associated with table 'users'
var User = this.sequelize.define('user', {
  first_name: Sequelize.STRING,
  last_name: Sequelize.STRING
});

// creates a 'userId' field in the Product model
Product.belongsTo(User);

// long way
  //create a new User, saves it to the DB
User.create({ 
    first_name: 'Mick', 
    last_name: 'Broadstone'
  })
  .then(user => {
    // once user is created, create a product, and fill in the userId field manually
    Product.create({
      title: 'Chair',
      userId: user.id
    })
  })

// nicer way
Product.create({
  title: 'Desk',
  // provide a 'user' field where you provide a user definition
  user: {
    first_name: 'Ben',
    last_name: 'Cohen'
  }
}, {
  include: [ User ]    // include a data dependency
});
// Product is created, but before it can fill in userId it creates a new User
// with the provided data and automatically adds that user.id value into the Products
// userId column


// Note that both ways are really equivalent, so neither is truly nicer, its
// a matter of choice

/*-------------------------- The Database ---------------------------*
|                           -------------                            |
|                                                                    |
|         products       |                users                      |
|          --------      |               ------                      |
| id   title    userId   |    id      first_name     last_name       |
| --   -----    ------   |    --      ----------     ---------       |
| 44   'Chair'    12     |    12        'Mick'      'Boradstone'     |
| 56   'Desk'     32     |    32        'Ben'        'Cohen'         |
|                        |                                           |
|                        |                                           |
*-------------------------------------------------------------------*/