Installation

Sequelize is available via NPM.

$ npm install --save sequelize
# And one of the following:
$ npm install --save pg pg-hstore
$ npm install --save mysql // For both mysql and mariadb dialects
$ npm install --save sqlite3
$ npm install --save tedious // MSSQL

Setting up a connection

Sequelize will setup a connection pool on initialization so you should ideally only ever create one instance per database.

var sequelize = new Sequelize('database', 'username', 'password', {
  host: 'localhost',
  dialect: 'mysql'|'mariadb'|'sqlite'|'postgres'|'mssql',
  pool: {
    max: 5,
    min: 0,
    idle: 10000
  },
  // SQLite only
  storage: 'path/to/database.sqlite'
});
// Or you can simply use a connection uri
var sequelize = new Sequelize('postgres://user:pass@example.com:5432/dbname');

The Sequelize constructor takes a whole slew of options that are available via the API reference.

Your first model

Models are defined with sequelize.define('name', {attributes}, {options}).

var User = sequelize.define('user', {
  firstName: {
    type: Sequelize.STRING,
    field: 'first_name' // Will result in an attribute that is firstName when user facing but first_name in the database
  },
  lastName: {
    type: Sequelize.STRING
  }
}, {
  freezeTableName: true // Model tableName will be the same as the model name
});
User.sync({force: true}).then(function () {
  // Table created
  return User.create({
    firstName: 'John',
    lastName: 'Hancock'
  });
});

Many more options can be found in the Model API reference

Application wide model options

The Sequelize constructor takes a define option which will be used as the default options for all defined models.

var sequelize = new Sequelize('connectionUri', {
  define: {
    timestamps: false // true by default
  }
});
var User = sequelize.define('user', {}); // timestamps is false by default
var Post = sequelize.define('post', {}, {
  timestamps: true // timestamps will now be true
});

Promises

Sequelize uses promises to control async control-flow. If you are unfamiliar with how promises work, now might be a good time to brush up on them, here and here

Basically a promise represents a value which will be present at some point - "I promise you I will give you a result or an error at some point". This means that

// DON'T DO THIS
user = User.findOne()
console.log(user.get('firstName'));

will never work! This is because user is a promise object, not a data row from the DB. The right way to do it is:

User.findOne().then(function (user) {
    console.log(user.get('firstName'));
});

Once you've got the hang of what promises are and how they work, use the bluebird API reference as your go to tool. In particular, you'll probably be using .all a lot.