Hooks (also known as callbacks or lifecycle events), are functions which are called before and after calls in sequelize are executed. For example, if you want to always set a value on a model before saving it, you can add a beforeUpdate hook.

For a full list of hooks, see Hooks API.

Order of Operations

(1)
  beforeBulkCreate(instances, options, fn)
  beforeBulkDestroy(options, fn)
  beforeBulkUpdate(options, fn)
(2)
  beforeValidate(instance, options, fn)
(-)
  validate
(3)
  afterValidate(instance, options, fn)
  - or -
  validationFailed(instance, options, error, fn)
(4)
  beforeCreate(instance, options, fn)
  beforeDestroy(instance, options, fn)
  beforeUpdate(instance, options, fn)
(-)
  create
  destroy
  update
(5)
  afterCreate(instance, options, fn)
  afterDestroy(instance, options, fn)
  afterUpdate(instance, options, fn)
(6)
  afterBulkCreate(instances, options, fn)
  afterBulkDestroy(options, fn)
  afterBulkUpdate(options, fn)

Declaring Hooks

Arguments to hooks are passed by reference. This means, that you can change the values, and this will be reflected in the insert / update statement. A hook may contain async actions - in this case the hook function should return a promise.

There are currently three ways to programmatically add hooks:

// Method 1 via the .define() method
var User = sequelize.define('user', {
  username: DataTypes.STRING,
  mood: {
    type: DataTypes.ENUM,
    values: ['happy', 'sad', 'neutral']
  }
}, {
  hooks: {
    beforeValidate: function(user, options) {
      user.mood = 'happy'
    },
    afterValidate: function(user, options) {
      user.username = 'Toni'
    }
  }
})

// Method 2 via the .hook() method
User.hook('beforeValidate', function(user, options) {
  user.mood = 'happy'
})

User.hook('afterValidate', function(user, options) {
  return sequelize.Promise.reject("I'm afraid I can't let you do that!")
})

// Method 3 via the direct method
User.beforeCreate(function(user, options) {
  return hashPassword(user.password).then(function (hashedPw) {
    user.password = hashedPw;
  });
})

User.afterValidate('myHookAfter', function(user, options, fn) {
  user.username = 'Toni'
})

Removing hooks

Only a hook with name param can be removed.

var Book = sequelize.define('book', {
  title: DataTypes.STRING
})

Book.addHook('afterCreate', 'notifyUsers', function(book, options) {
  // ...
})

Book.removeHook('afterCreate', 'notifyUsers')

Global / universal hooks

Global hooks are hooks which are run for all models. They can define behaviours that you want for all your models, and are especially useful for plugins. They can be defined in two ways, which have slightly different semantics:

Sequelize.options.define (default hook)

var sequelize = new Sequelize(..., {
    define: {
        hooks: {
            beforeCreate: function () {
                // Do stuff
            }
        }
    }
});

This adds a default hook to all models, which is run if the model does not define its own beforeCreate hook:

var User = sequelize.define('user');
var Project = sequelize.define('project', {}, {
    hooks: {
        beforeCreate: function () {
            // Do other stuff
        }
    }
});

User.create() // Runs the global hook
Project.create() // Runs its own hook (because the global hook is overwritten)

Sequelize.addHook (permanent hook)

sequelize.addHook('beforeCreate', function () {
    // Do stuff
});

This hooks is always run before create, regardless of whether the model specifies its own beforeCreate hook:

var User = sequelize.define('user');
var Project = sequelize.define('project', {}, {
    hooks: {
        beforeCreate: function () {
            // Do other stuff
        }
    }
});

User.create() // Runs the global hook
Project.create() // Runs its own hook, followed by the global hook

Local hooks are always run before global hooks.

Instance hooks

The following hooks will emit whenever you're editing a single object

beforeValidate
afterValidate or validationFailed
beforeCreate / beforeUpdate  / beforeDestroy
afterCreate / afterUpdate / afterDestroy

// ...define ...
User.beforeCreate(function(user) {
  if (user.accessLevel > 10 && user.username !== "Boss") {
    throw new Error("You can't grant this user an access level above 10!")
  }
})

This example will return an error:

User.create({username: 'Not a Boss', accessLevel: 20}).catch(function(err) {
  console.log(err) // You can't grant this user an access level above 10!
})

The following example would return successful:

User.create({username: 'Boss', accessLevel: 20}).then(function(user) {
  console.log(user) // user object with username as Boss and accessLevel of 20
})

Model hooks

Sometimes you'll be editing more than one record at a time by utilizing the bulkCreate, update, destroy methods on the model. The following will emit whenever you're using one of those methods.

beforeBulkCreate / beforeBulkUpdate / beforeBulkDestroy
afterBulkCreate / afterBulkUpdate / afterBulkDestroy

If you want to emit hooks for each individual record, along with the bulk hooks you can pass individualHooks: true to the call.

Model.destroy({ where: {accessLevel: 0}, individualHooks: true})
// Will select all records that are about to be deleted and emit before- + after- Destroy on each instance

Model.update({username: 'Toni'}, { where: {accessLevel: 0}, individualHooks: true})
// Will select all records that are about to be updated and emit before- + after- Update on each instance

Some model hooks have two or three parameters sent to each hook depending on it's type.

Model.beforeBulkCreate(function(records, fields) {
  // records = the first argument sent to .bulkCreate
  // fields = the second argument sent to .bulkCreate
})

Model.bulkCreate([
  {username: 'Toni'}, // part of records argument
  {username: 'Tobi'} // part of records argument
], ['username'] /* part of fields argument */)

Model.beforeBulkUpdate(function(attributes, where) {
  // attributes = first argument sent to Model.update
  // where = second argument sent to Model.update
})

Model.update({gender: 'Male'} /*attributes argument*/, { where: {username: 'Tom'}} /*where argument*/)

Model.beforeBulkDestroy(function(whereClause) {
  // whereClause = first argument sent to Model.destroy
})

Model.destroy({ where: {username: 'Tom'}} /*whereClause argument*/)

If you use Model.bulkCreate(...) with the updatesOnDuplicate option, changes made in the hook to fields that aren't given in the updatesOnDuplicate array will not be persisted to the database. However it is possible to change the updatesOnDuplicate option inside the hook if this is what you want.

// Bulk updating existing users with updatesOnDuplicate option
Users.bulkCreate([{ id: 1, isMemeber: true}, 
                 { id: 2, isMember: false}], 
                 { updatesOnDuplicate: ['isMember']})

User.beforeBulkCreate(function (users, options) {
  users.forEach(function (user) {
    if (user.isMember) {
      user.memberSince = new Date()
    }
  })

  // Add memberSince to updatesOnDuplicate otherwise the memberSince date wont be
  // saved to the database
  options.updatesOnDuplicate.push('memberSince')
})

Associations

For the most part hooks will work the same for instances when being associated except a few things

1. When using add/set functions the beforeUpdate/afterUpdate hooks will run.
2. The only way to call beforeDestroy/afterDestroy hooks are on associations with onDelete: 'cascade' and the option hooks: true. For instance:

var Projects = sequelize.define('projects', {
  title: DataTypes.STRING
})

var Tasks = sequelize.define('tasks', {
  title: DataTypes.STRING
})

Projects.hasMany(Tasks, { onDelete: 'cascade', hooks: true })
Tasks.belongsTo(Projects)

This code will run beforeDestroy/afterDestroy on the Tasks table. Sequelize, by default, will try to optimize your queries as much as possible. When calling cascade on delete, Sequelize will simply execute a

DELETE FROM `table` WHERE associatedIdentifier = associatedIdentifier.primaryKey

However, adding hooks: true explicitly tells Sequelize that optimization is not of your concern and will perform a SELECT on the associated objects and destroy each instance one by one in order to be able to call the hooks with the right parameters.

If your association is of type n:m, you may be interested in firing hooks on the through model when using the remove call. Internally, sequelize is using Model.destroy resulting in calling the bulkDestroy instead of the before/afterDestroy hooks on each through instance.

This can be simply solved by passing {individualHooks: true} to the remove call, resulting on each hook to be called on each removed through instance object.

A Note About Transactions

Note that many model operations in Sequelize allow you to specify a transaction in the options parameter of the method. If a transaction is specified in the original call, it will be present in the options parameter passed to the hook function. For example, consider the following snippet:

// Here we use the promise-style of async hooks rather than
// the callback.
User.hook('afterCreate', function(user, options) {
  // 'transaction' will be available in options.transaction

  // This operation will be part of the same transaction as the
  // original User.create call.
  return User.update({
    mood: 'sad'
  }, {
    where: {
      id: user.id
    },
    transaction: options.transaction
  });
});


sequelize.transaction(function(t) {
  User.create({
    username: 'someguy',
    mood: 'happy',
    transaction: t
  });
});

If we had not included the transaction option in our call to User.update in the preceding code, no change would have occurred, since our newly created user does not exist in the database until the pending transaction has been committed.

Internal Transactions

It is very important to recognize that sequelize may make use of transactions internally for certain operations such as Model.findOrCreate. If your hook functions execute read or write operations that rely on the object's presence in the database, or modify the object's stored values like the example in the preceding section, you should always specify { transaction: options.transaction }.

If the hook has been called in the process of a transacted operation, this makes sure that your dependent read/write is a part of that same transaction. If the hook is not transacted, you have simply specified { transaction: null } and can expect the default behaviour.