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Upgrade to V4

Sequelize V4 is a major release and it introduces new features and breaking changes. Majority of sequelize codebase has been refactored to use ES2015 features. The following guide lists some of the changes to upgrade from v3 to v4. See the Changelog for full list of changes.

Breaking Changes

  • Node version: To use new ES2015 features, we now require at least Node 4. From now on, we will support all current LTS versions of Node.
  • The counter cache plugin, and consequently the counterCache option for associations has been removed. The same behaviour can be achieved using afterCreate and afterDelete hooks.
  • Removed MariaDB dialect. This was just a thin wrapper around MySQL, so using dialect: 'mysql' instead should work with no further changes
  • Removed default REPEATABLE_READ transaction isolation. The isolation level now defaults to that of the database. Explicitly pass the required isolation level when initiating the transaction.
  • Removed support for pool: false. To use a single connection, set pool.max to 1.
  • Removed support for old connection pooling configuration keys. Instead of

    pool: {
      maxIdleTime: 30000,
      minConnections: 20,
      maxConnections: 30


    pool: {
      idle: 30000,
      min: 20,
      max: 30
  • (MySQL) BIGINT now gets converted to string when number is too big

  • (MySQL) DECIMAL and NEWDECIMAL types now returned as String unless
    dialectOptions: {
      decimalNumbers: true
    is specified.
  • Removed support for referencesKey, use a references object
    references: {
        key: '',
        model: ''
  • classMethods and instanceMethods are removed.


    const Model = sequelize.define('Model', {
    }, {
        classMethods: {
            associate: function (model) {...}
        instanceMethods: {
            someMethod: function () { ...}


    const Model = sequelize.define('Model', {
    // Class Method
    Model.associate = function (models) {
        ...associate the models
    // Instance Method
    Model.prototype.someMethod = function () {..}
  • Model.Instance and instance.Model are removed. To access the Model from an instance, simply use instance.constructor. The Instance class (Model.Instance) is now the Model itself.
  • Sequelize now uses an independent copy of bluebird library.

    • Promises returned by sequelize are now instances of Sequelize.Promise instead of global bluebird Promise.
    • The CLS patch does not affect global bluebird promise. Transaction will not automatically get passed to methods when used with Promise.all and other bluebird methods. Explicitly patch your bluebird instance to get CLS to work with bluebird methods.

      $ npm install --save cls-bluebird
      const Promise = require('bluebird');
      const Sequelize = require('sequelize');
      const cls = require('continuation-local-storage');
      const ns = cls.createNamespace('transaction-namespace');
      const clsBluebird = require('cls-bluebird');
      clsBluebird(ns, Promise);
  • Sequelize.Validator is now an independent copy of validator library
  • DataTypes.DECIMAL returns string for MySQL and Postgres.
  • DataTypes.DATE now uses DATETIMEOFFSET instead of DATETIME2 sql datatype in case of MSSQL to record timezone. To migrate existing DATETIME2 columns into DATETIMEOFFSET, see #7201.
  • options.order now only accepts values with type of array or Sequelize method. Support for string values (ie {order: 'name DESC'}) has been deprecated.
  • With BelongsToMany relationships add/set/create setters now set through attributes by passing them as options.through (previously second argument was used as through attributes, now it's considered options with through being a sub option)


    user.addProject(project, { status: 'started' })


    user.addProject(project, { through: { status: 'started' }})
  • DATEONLY now returns string in YYYY-MM-DD format rather than Date type

  • Model.validate instance method now runs validation hooks by default. Previously you needed to pass { hooks: true }. You can override this behavior by passing { hooks: false }
  • The resulting promise from the Model.validate instance method will be rejected when validation fails. It will fulfill when validation succeeds.
  • Raw options for where, order and group like where: { $raw: '..', order: [{ raw: '..' }], group: [{ raw: '..' }] } have been removed to prevent SQL injection attacks.
  • Sequelize.Utils is not longer part of the public API, use it at your own risk
  • Hooks should return Promises now. Callbacks are deprecated.

New features

  • Initial version of sequelize.sync({ alter: true }) has been added and uses ALTER TABLE commands to sync tables. Migrations are still preferred and should be used in production.
  • Adding and removing database contraints are now supported. Existing primary, foreignKey and other contraints can now be added/removed using migrations - See more.
  • Instances (database rows) are now instances of the model, instead of being an instance of a separate class. This means you can replace User.build() with new User() and sequelize.define(attributes, options) with
    class User extends Sequelize.Model {}
    User.init(attributes, options)
    You can then define custom methods, class methods and getters/setter directly in the class. This also enables more usage patterns, for example with decorators.
  • Added DEBUG support. You can now use DEBUG=sequelize* node app.js to enable logging for all sequelize operations. To filter logged queries, use DEBUG=sequelize:sql:mssql sequelize:connection* to log generated SQL queries, connection info etc.
  • JSON datatype support has been added for SQLite
  • UPSERT is now supported on MSSQL using MERGE statement.
  • Transactions are now fully supported on MSSQL.
  • Filtered indexes are now supported on MSSQL dialect.
      ['firstname', 'lastname'],
        where: {
          lastname: {
            $ne: null