A gem for using Sequel with Rails 4.x and 5.x
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This gem provides the railtie that allows sequel to hook into Rails (4.x and 5.x) and thus behave like a rails framework component. Just like activerecord does in rails, sequel-rails uses the railtie API to hook into rails. The two are actually hooked into rails almost identically.

The code for this gem was initially taken from the excellent dm-rails project.

This was originally a fork of brasten's sequel-rails that has been updated to support newer versions of rails.

Since January 2013, we've become the official maintainers of the gem after brasten proposed us.

Using sequel-rails

Using sequel with Rails (4.x or 5.x) requires a couple minor changes.

First, add the following to your Gemfile (after the Rails lines):

# depending on you database
gem "pg"        # for PostgreSQL
gem "mysql2"    # for MySQL
gem "sqlite3"   # for Sqlite

gem "sequel-rails"

... be sure to run "bundle install" if needed!

Secondly, you'll need to require the different Rails components separately in your config/application.rb file, and not require ActiveRecord. The top of your config/application.rb will probably look something like:

# require 'rails/all'

# Instead of 'rails/all', require these:
require "active_model/railtie"
require "active_job/railtie"
# require "active_record/railtie"
require "action_controller/railtie"
require "action_mailer/railtie"
require "action_view/railtie"
require "action_cable/engine"
require "sprockets/railtie"
require "rails/test_unit/railtie"

Then you need to get rid of ActiveRecord configurations, that is if you didn't generate the new app with -O (or the long form --skip-active-record):

For example in a fresh Rails, you would need to remove those lines:

line 18:  Rails.application.config.active_record.belongs_to_required_by_default = true
line 38:  config.active_record.migration_error = :page_load
line 85:  config.active_record.dump_schema_after_migration = false

Starting with sequel-rails 0.4.0.pre3 we don't change default Sequel behaviour nor include any plugin by default, if you want to get back the previous behaviour, you can create a new initializer (eg: config/initializers/sequel.rb) with content:

require "sequel_rails/railties/legacy_model_config"

After those changes, you should be good to go!

Features provided by sequel-rails

  1. Connection management:

    sequel-rails will initiate the Sequel connection mechanism based on your configuration in database.yml.

  2. Generators:

    You can use them just like ActiveRecord's ones:


    rails generate migration create_admin_users
    # Or
    rails generate migration CreateAdminUsers


    rails generate model User email:string


    rails generate observer User


    rails generate sequel:session_migration
  3. Rake tasks similar to ActiveRecord, see Available sequel specific rake tasks

  4. Add some Sequel and sequel-rails specific exceptions to ActionDispatch's rescue_responses

    Sequel::Plugins::RailsExtensions::ModelNotFound is mapped to :not_found

    Sequel::NoMatchingRow is mapped to :not_found

    Sequel::ValidationFailed is mapped to :unprocessable_entity

    Sequel::NoExistingObject is mapped to :unprocessable_entity

  5. Add a i18n_scope method to Sequel::Model which respond with "sequel". This is used by ActiveModel.

  6. Adding Sequel to ActiveSupport::LogSubscriber. This is what allows you to see SQL queries in the log and also allows us to implement the next item.

  7. Add a hook in ActionController::Base so that the sum of SQL queries time for the current action is reported as DB for the controller's line in logs.

  8. Provide a ActionDispatch::Session::SequelStore similar to the ActiveRecord one, which stores sessions in database backed by a Sequel model.


You can configure some options with the usual rails mechanism, in config/application.rb and/or in config/environments/*.rb.

    # Allowed options: :sql, :ruby.
    config.sequel.schema_format = :sql

    # Whether to dump the schema after successful migrations.
    # Defaults to false in production and test, true otherwise.
    config.sequel.schema_dump = true

    # These override corresponding settings from the database config.
    config.sequel.max_connections = 16
    config.sequel.search_path = %w(mine public)

    # Configure whether database's rake tasks will be loaded or not.
    # If passed a String or Symbol, this will replace the `db:` namespace for
    # the database's Rake tasks.
    # ex: config.sequel.load_database_tasks = :sequel
    #     will results in `rake db:migrate` to become `rake sequel:migrate`
    # Defaults to true
    config.sequel.load_database_tasks = false

    # This setting disabled the automatic connect after Rails init
    config.sequel.skip_connect = true

    # If you want to use a specific logger
    config.sequel.logger = MyLogger.new($stdout)

The connection settings are read from the file config/database.yml and is expected to be similar to ActiveRecord's format.

Here's some examples:

  1. For PostgreSQL:

      adapter: postgresql
      database: a_database_name
      user: user_name # Also accept 'username' as key, if both are present 'username' is used
      password: password
      host: # Optional
      port: 5432 # Optional
      owner: owner_name # Optional
      encoding: utf8 # Optional, also accept 'charset' as key, if both are present 'encoding' is used (defaults to 'utf8')
      maintenance_db: template2 # Optional
      locale: en_US.UTF-8 # Optional, equivalent to setting 'collation' and 'ctype' to the same value
      collation: en_US.UTF-8 # Optional
      ctype: en_US.UTF-8 # Optional
      template: template1 # Optional
      tablespace: non_default_tablespace_name # Optional
      max_connections: 20 # Optional, also accept 'pool' as key, if both are present 'max_connections' is used (default to nil, Sequel default is 4)
      url: "postgres://myuser:mypass@host/somedatabase" # Optional, if present it's passed to `Sequel.connect` with other config as options
                                                        # If url is not set in config file, environment variable `DATABASE_URL` is used
  2. For MySQL:

      adapter: mysql # Also accept mysql2
      database: a_database_name
      user: user_name # Also accept 'username' as key, if both are present 'username' is used
      password: password
      host: # Optional
      port: 5432 # Optional
      charset: latin1 # Optional (defaults to 'utf8')
      collation: latin1_general_ci # Optional (defaults to 'utf8_unicode_ci')
      url: "mysql://myuser:mypass@host/somedatabase" # Optional, if present it's passed to `Sequel.connect` with other config as options
                                                     # If url is not set in config file, environment variable `DATABASE_URL` is used
  3. For SQLite:

      adapter: sqlite # Also accept sqlite3
      database: db/mydatabase.sqlite # Path to db relative to Rails root

For in memory testing:

  adapter: sqlite # Also accept sqlite3
  database: ":memory:"

Enabling plugins

If you want to enable plugins for all your models, you should use the after_connect configuration option in config/application.rb (0.6.2+):

    config.sequel.after_connect = proc do
      Sequel::Model.plugin :timestamps, update_on_create: true

This will ensure that these plugins are loaded before any Sequel models are loaded. Loading plugins into Sequel::Model after subclasses are already created is not supported by Sequel. You can also load extensions in after_connect or perform any custom actions that you need.

Please note: some plugins require a dataset to work, which means they can't be added via Sequel::Model.plugin, they need to be added to a Sequel::Model subclass whose underlying table exists.

Using the SequelStore to store session in database

If you want to store your session in the database you can use the provided session store backed by a Sequel model. Edit your config/initializers/session.rb file and replace the existing code with:

YourAppName::Application.config.session_store :sequel_store

You can then generate a migration for the session table using the provided generator:

rails generate sequel:session_migration
rake db:migrate

Optionally if you want to use your own Sequel model to handle the session, you can do so in your config/initializers/session.rb:

ActionDispatch::Session::SequelStore.session_class = MyCustomSessionModelClass

Available sequel specific rake tasks

To get a list of all available rake tasks in your rails3 app, issue the usual in you app's root directory:

rake -T

or if you don't have hooks in place to run commands with bundle by default:

bundle exec rake -T

Once you do that, you will see the following rake tasks among others. These are the ones that sequel-rails added or replaced:

rake db:create[env]                   # Create the database defined in config/database.yml for the current Rails.env
rake db:create:all                    # Create all the local databases defined in config/database.yml
rake db:drop[env]                     # Create the database defined in config/database.yml for the current Rails.env
rake db:drop:all                      # Drops all the local databases defined in config/database.yml
rake db:force_close_open_connections  # Forcibly close any open connections to the test database
rake db:migrate                       # Migrate the database to the latest version
rake db:migrate:down                  # Runs the "down" for a given migration VERSION.
rake db:migrate:redo                  # Rollbacks the database one migration and re migrate up.
rake db:migrate:reset                 # Resets your database using your migrations for the current environment
rake db:migrate:up                    # Runs the "up" for a given migration VERSION.
rake db:reset                         # Drops and recreates the database from db/schema.rb for the current environment and loads the seeds.
rake db:schema:dump                   # Create a db/schema.rb file that can be portably used against any DB supported by Sequel
rake db:schema:load                   # Load a schema.rb file into the database
rake db:seed                          # Load the seed data from db/seeds.rb
rake db:setup                         # Create the database, load the schema, and initialize with the seed data
rake db:test:prepare                  # Prepare test database (ensure all migrations ran, drop and re-create database then load schema). This task can be run in the same invocation as other task (eg: rake db:migrate db:test:prepare).

Note on Patches/Pull Requests

  • Fork the project.
  • Make your feature addition or bug fix.
  • Add specs for it. This is important so I don't break it in a future version unintentionally.
  • Commit, do not mess with rakefile, version, or history. (if you want to have your own version, that is fine but bump version in a commit by itself I can ignore when I pull)
  • Send me a pull request. Bonus points for topic branches.

The sequel-rails team

  • Jonathan Tron (JonathanTron) - Current maintainer
  • Joseph Halter (JosephHalter) - Current maintainer

Previous maintainer

Original project:

  • Brasten Sager (brasten) - Project creator


Improvements have been made by those awesome contributors:

  • Benjamin Atkin (@benatkin)
  • Gabor Ratky (@rgabo)
  • Joshua Hansen (@binarypaladin)
  • Arron Washington (@radicaled)
  • Thiago Pradi (@tchandy)
  • Sascha Cunz (@scunz)
  • Brian Donovan (@eventualbuddha)
  • Jack Danger Canty (@JackDanger)
  • Ed Ruder (@edruder)
  • Rafał Rzepecki (@dividedmind)
  • Sean Sorrell (@rudle)
  • Saulius Grigaliunas (@sauliusg)
  • Jacques Crocker (@railsjedi)
  • Eric Strathmeyer (@strathmeyer)
  • Jan Berdajs (@mrbrdo)
  • Robert Payne (@robertjpayne)
  • Kevin Menard (@nirvdrum)
  • Chris Heisterkamp (@cheister)
  • Tamir Duberstein (@tamird)
  • shelling (@shelling)
  • a3gis (@a3gis)
  • Andrey Chernih (@andreychernih)
  • Nico Rieck (@gix)
  • Alexander Birkner (@BirknerAlex)
  • kr3ssh (@kressh)
  • John Anderson (@djellemah)
  • Larivact (@Larivact)
  • Jan Berdajs (@mrbrdo)
  • Lukas Fittl (@lfittl)
  • Jordan Owens (@jkowens)
  • Pablo Herrero (@pabloh)
  • Henre Botha (@henrebotha)
  • Mohammad Satrio (@tyok)
  • Gencer W. Genç (@gencer)
  • Steve Hoeksema (@steveh)
  • Jester (@Jesterovskiy)
  • ckoenig (@ckoenig)


The dm-rails team wrote most of the original code, I just sequel-ized it, but since then most of it has been either adapted or rewritten.


Copyright (c) 2010-2013 The sequel-rails team. See LICENSE for details.