When generating a new Sequent project the configuration can be found in config/initializers/sequent.rb. You are free to determine your own location as long as you require the file at startup of your application.

There are many configuration options, but mostly you can stick to the defaults. With that thought in mind this chapter is divided into 3 sections:

  1. The minimum configuration you need
  2. Configuration options you will likely want to change
  3. The complete overview of options. Basically the rest.

Minimum configuration

As a bare minimum you need:

require './db/migrations'

Sequent.configure do |config|
 config.migrations_class_name = 'Migrations'

 config.command_handlers = [

 config.event_handlers = [

The migration_class_name is the name of the class used to define your Migrations. See the Migrations chapter for an in-depth explanation.

Frequently used configuration:

Sequent.configure do |config|
  # minimum config omitted

  # common config options

  config.command_filters = [

  config.number_of_replay_processes = 4

  config.logger = Logger.new(STDOUT)


CommandFilters can be used to enforce certain criteria are met before executing commands. Typical concerns are authorization in a user based application. A filter must implement the method execute(command). If any of the CommandFilters raises an Exception then execution is aborted for all passed Commands.


class AdminFilter
  def execute(command)
    fail NotAnAdmin unless is_allowed?(command.user_id, command.class)

  # only admin may execute admin commands
  def is_allowed?(user_id, command_class)
    return false if !UserRecord.is_admin?(user_id) && command_class <= AdminCommand
    return true

Sequent.configure do |config|
  config.command_filters = [


The number of processes used to replay the events when doing a Migration. By default this is 4. This should be adjusted to the capactiy of your server running the Migration.


The ruby Logger used by Sequent.

Complete configuration

For the most recent possibilities please check the Sequent::Configuration implementation.

Option Meaning Default Value
aggregate_repository The AggregateRepository Sequent::Core::AggregateRepository.new
event_store The EventStore Sequent::Core::EventStore.new
command_service The CommandService Sequent::Core::CommandService.new
event_record_class The class mapped to the event_records Sequent::Core::EventRecord
stream_record_class The class mapped to the stream_records table Sequent::Core::StreamRecord
snapshot_event_class The event class marking something as a Snapshot event Sequent::Core::SnapshotEvent
event_record_hooks_class The class with EventRecord life cycle hooks Sequent::Core::EventRecordHooks
transaction_provider The transaction provider used by the CommandService Sequent::Core::Transactions::ActiveRecordTransactionProvider.new
event_publisher The EventPublisher used by the EventStore. Sequent::Core::EventPublisher.new
command_handlers The list of CommandHandlers Empty
command_filters The list of CommandFilters Empty
event_handlers The list of Projectors and Workflows Empty
uuid_generator The AggregateRepository. Mainly useful for testing false
disable_event_handlers If true no event_handlers will be called Sequent::Core::EventStore.new
migration_sql_files_directory The location of the sql files for Migrations db/tables
view_schema_name The name of the view_schema in which the projections are created. view_schema
offline_replay_persistor_class The class used to persist the the Projectors during the offline migration part.. Sequent::Core::Persistors::ActiveRecordPersistor
online_replay_persistor_class The class used to persist the the Projectors. Sequent::Core::Persistors::ActiveRecordPersistor
number_of_replay_processes The number of process used while offline migration 4
database_config_directory The directory in which db config can be found db
database_schema_directory The directory in which db schema and migrations can be found db
event_store_schema_name The name of the db schema in which the EventStore is installed sequent_schema
strict_check_attributes_on_apply_events Whether or not sequent should fail on calling apply with invalid attributes. false. Will be enabled by default in the next major release.
migrations_class_name The name of the class containing the migrations Empty
versions_table_name The name of the table in which Sequent checks which migration version is currently active sequent_versions
replayed_ids_table_name The name of the table in which Sequent keeps track of which events are already replayed during a migration sequent_replayed_ids
error_locale_resolver A lambda that returns the desired locale for command validation errors -> { I18n.locale || :en }