Code Quality Rank: L5
Programming language: Ruby
License: MIT License
Latest version: v1.3.1

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Milia is a multi-tenanting gem for Ruby on Rails applications. Milia supports Devise.

You are viewing the documentation for using milia with Rails 5.x applications.
If you want to use Rails 4.2.x instead please switch to the Rails 4.x branch.

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  • Milia is a solid choice for (SaaS) applications which are used by more than one tenant (i.e. companies or organizations) and is tailored for common use cases of multi-tenanted applications.
  • Milia allows to save the data of all tenants in the same database and enforces row based separation of the tenant data.
  • Milia uses the devise gem for user authentication and registration.

Milia highlights

  • Transparent to the main application code
  • Symbiotic with user authentication (supports devise out of the box)
  • Raises exceptions upon attempted illegal access
  • Enforces tenanting (not allow sloppy access to all tenant records)
  • Allows application flexibility upon new tenant sign-up, usage of eula information, etc
  • As non-invasive (as possible) to Rails code
  • Uses row-based tenanting (for [good reasons](README_DETAILS.md#row-based-vs-schema-based-tenanting))
  • Uses default_scope to enforce tenanting
  • See Milia in action in the Sample App

Basic concepts

Tenants == Organizations with Users / Members

A tenant is an organization with many members (users). Initially a user creates a new organization (tenant) and becomes its first member (and usually admin). Then he invites further members who can then login and join the tenant. Milia ensures that users can only access data of their own tenant (organization).

Tenanted models

Models which belong to a certain tenant (organization).
Add acts_as_tenant to the model body to activate tenanting for this model.
Most of your tables (except for pure join tables, users, and tenants) should be tenanted. Every record of a tenanted table needs to have a tenant_id set. Milia takes care of this.

Universal models

Models which aren't specific to a tenant (organization) but have system wide relevance. Add acts_as_universal to the model body to mark them as universal models.
Universal tables never contain critical user/company information. The devise user table must be universal and should only contain email, encrypted password, and devise-required data. All other user data (name, phone, address, etc) should be broken out into a tenanted table called members (Member belongs_to :user, User has_one :member). The same applies for organization (account or company) information. A record of a universal table must have tenant_id set to nil. Milia takes care of this.

Join tables

Pure join tables (has_and_belongs_to_many HABTM associations) are neither Universal nor Tenanted.

Tutorials + Documentation

  • Up to date starting point is the README you're currently viewing.
  • For more details on token authentication, exceptions, callbacks, devise setup etc. have a look at the [additional README_DETAILS](README_DETAILS.md).
  • Tutorial: There's a good Milia tutorial at myrailscraft.
  • Check out the general [three-part blog post]((http://myrailscraft.blogspot.com/2013/05/multi-tenanting-ruby-on-rails.html).) about Multi-tenanting Ruby on Rails Applications on Heroku.

Sample app

You can get a sample app up and running yourself using an easy, interactive RailsApp generator and an according Milia generator. If desired the generator can also prepare everything for you to push your app to Heroku. The sample app uses devise with the invite_member capability (and optionally recaptcha for new account sign-ups). It creates skeleton user, tenant and member models.

Simply follow the following steps:

mkdir milia-sample-app
cd milia-sample-app
rvm use ruby-2.3.1@milia-sample-app --ruby-version --create
gem install rails
rails new . -m https://raw.github.com/RailsApps/rails-composer/master/composer.rb

An interactive setup starts which asks you some questions.

  • Choose "Build a RailsApps example application"
  • Choose "rails-devise" as the example template
  • Choose Template engine "HAML"
  • Choose "Devise with default modules"
  • Choose the other options depending on your needs

After the setup finished add to your Gemfile:
gem 'milia'

Install milia: bundle install

In app/controllers/application_controller.rb add the following line immediately after protect_from_forgery:
before_action :authenticate_tenant!

Run the following commands:

spring stop
rails g milia:install --org_email='[email protected]' --skip_devise_generators=true
  • Remove lower line "before_action :authenticate_tenant!" which has been added to app/controllers/application_controller.rb by the milia generator.
  • Remove the lines @extend .text-xs-center; (if any) from the file 1st_load_framework.css.scss.
  • Remove the file app/views/devise/registrations/new.html.erb

Setup the database: rake db:drop db:create db:migrate

Start the server: rails server

Open in your browser. You're ready to go!

Previous sample app

For your reference: An outdated milia+devise sample app can be found at https://github.com/dsaronin/sample-milia-app and is live on Heroku: http://sample-milia.herokuapp.com
The according instructions on how to generate this sample app can be found at [doc/sample.sh](doc/sample.sh).

There are also outdated step-by-step instructions for setting this sample app up manually at [doc/manual_sample.sh](doc/manual_sample.sh).

  • Step 1: Sample with simple devise only
  • Step 2: Add milia for complete tenanting
  • Step 3: Add invite_member capability


Adding milia to a new application

The quickest way: Follow the simple instructions of the chapter Sample App to generate a new app which uses devise+milia.

Add milia to an existing application

The recommended way to add multi-tenanting with milia to an existing app is to bring up the Sample App, get it working and then graft your app onto it. This ensures that the Rails+Devise setup works correctly.

Go step by Step

Don't try to change everything at once! Don't be a perfectionist and try to bring up a fully written app at once!

Just follow the instructions for creating the sample, exactly, step-by-step. Get the basics working. Then change, adapt, and spice to taste.

Bare minimal manual setup

(If you generated a [Sample App](Sample App) all of the following steps have been done already.)

Add to your Gemfile:

  gem 'milia', '~>1.3'

Then run the milia generator:

  $ bundle install
  $ rails g milia:install --org_email='<your smtp email for dev work>'

Note: The milia generator has an option to specify an email address to be used for sending emails for confirmation and account activation.

For an in depth explanation of what the generator does have a look at [README_DETAILS](README_DETAILS.md).

Make any changes required to the generated migrations, then:

  $ rake db:create
  $ rake db:migrate

Application controller

app/controllers/application_controller.rb add the following line IMMEDIATELY AFTER line 4 protect_from_forgery

  before_action :authenticate_tenant!   # authenticate user and sets up tenant

  rescue_from ::Milia::Control::MaxTenantExceeded,   :with => :max_tenants
  rescue_from ::Milia::Control::InvalidTenantAccess, :with => :invalid_tenant

Setup base models

  • Necessary models: User, Tenant
  • Necessary migrations: user, tenant, tenants_users (join table)

Generate the tenant migration

  $ rails g model tenant tenant:references name:string:index

Generate the tenants_users join table migration

  $ rails g migration CreateTenantsUsersJoinTable tenants users

EDIT: db/migrate/20131119092046_create_tenants_users_join_table.rb then uncomment the first index line as follows: t.index [:tenant_id, :user_id]

ALL models require a tenanting field, whether they are to be universal or to be tenanted. So make sure you have migrations for all models which add the following:


  t.references :tenant

Tenanted models also require indexes for the tenant field.

  add_index :<tablename>, :tenant_id

BUT: Do not add any belongs_to :tenant statements into any of your models. milia will do that for all. However it makes sense to add into your app/models/tenant.rb file one line per tenanted model such as the following (replacing with your model's name):

  has_many  :<model>s, dependent: :destroy

The reason for this is that if you wish to have a master destroy tenant action, it will also remove all related tenanted tables and records automatically.

Do NOT add a reference to the user model such as

  has_many  :users, dependent: :destroy

because it produces errors.

Designate which model determines the account

Add the following acts_as_... to designate which model will be used as the key into tenants_users to find the tenant for a given user. Only designate one model in this manner e.g.:


  class User < ActiveRecord::Base


Designate which model determines the tenant

Add acts_as_universal_and_determines_tenant to designate which model will be used as the tenant model. It is this id field which designates the tenant for an entire group of users which exist within a single tenanted domain. Only designate one model in this manner.


  class Tenant < ActiveRecord::Base


Clean up tenant references

Clean up any generated belongs_to tenant references in all models which the generator might have generated (both acts_as_tenant and acts_as_universal).

Setup your custom models

Designate tenanted models

Add acts_as_tenant to ALL models which are to be tenanted. Example for a Post model:


  class Post < ActiveRecord::Base


Designate universal models

Add acts_as_universal to ALL models which are to be universal.

Role based authorization

You can use any role based authorization you like, e.g. the rolify gem with cancancan, authority or pundit.

Milia API Reference Manual

Get current tenant

From models call Tenant.current_tenant or Tenant.current_tenant_id to get the current tenant.

Change current tenant

Call set_current_tenant( tenant_id ) from controllers. (for example, if a member can belong to multiple tenants and wants to switch between them). NOTE: you will normally NEVER do this manually at the beginning of a session. Milia does this automatically during authorize_tenant!.

From background job, migration, rake task or console you can use Tenant.set_current_tenant(tenant). tenant can either be a tenant object or an integer tenant_id; anything else will raise an exception.

Use with caution! Normally tenants should never be changed from within models. It is only useful and safe when performed at the start of a background job (DelayedJob#perform), rake task, migration or start of rails console.

Iterate over tenants

To iterate over all instances of a certain model for all tenants do the following:

Tenant.find_each do |tenant|
  Animal.update_all alive: true

Rails Console

Note that even when running the console, (rails console) it will be run in multi-tenanting mode. Call Tenant.set_current_tenant(tenant_id) accordingly.

Milia callbacks

In some applications, you will want to set up commonly used variables used throughout your application, after a user and a tenant have been established and authenticated. This is optional and if the callback is missing, nothing will happen.


  def callback_authenticate_tenant
    # set_environment or whatever else you need for each valid session

Security / Caution

  • Milia designates a default_scope for all models (both universal and tenanted). Rails merges default_scopes if you use multiple default_scope declarations in your model, see ActiveRecord Docs. However by unscoping via unscoped you can accidentally remove tenant scoping from records. Therefore we strongly recommend to NOT USE default_scope at all.
  • Milia uses Thread.current[:tenant_id] to hold the current tenant for the existing Action request in the application.
  • SQL statements executed outside the context of ActiveRecord pose a potential danger; the current milia implementation does not extend to the DB connection level and so cannot enforce tenanting at this point.
  • The tenant_id of a universal model will always be forced to nil.
  • The tenant_id of a tenanted model will be set to the current_tenant of the current_user upon creation.
  • HABTM (has_and_belongs_to_many) associations don't have models; they shouldn't have id fields (setup as below) nor any field other than the joined references; they don't have a tenant_id field; rails will invoke the default_scope of the appropriate joined table which does have a tenant_id field.
  • Your code should never try to change or set the tenant_id of a record manually.
    • milia will not allow it
    • milia will check for deviance
    • milia will raise exceptions if it's wrong and
    • milia will override it to maintain integrity.
  • You use milia solely at your own risk!
    • When working with multi-tenanted applications you handle lots of data of several organizations/companies which means a special responsibility for protecting the data as well. Do in-depth security tests prior to publishing your application.

Contributing to milia

  • Check out the latest master to make sure the feature hasn't been implemented or the bug hasn't been fixed yet
  • Check out the issue tracker to make sure someone already hasn't requested it and/or contributed it
  • Fork the project
  • Start a feature/bugfix branch
  • Commit and push until you are happy with your contribution
  • Make sure to add tests for it. This is important so we don't break the feature in a future version unintentionally.
  • Please try not to mess with the Rakefile, version, or history. If you want to have your own version, or is otherwise necessary, that is fine, but please isolate to its own commit so we can cherry-pick around it.

Testing milia

For instructions on how to run and write tests for milia please consider the [README for testing](./test/README.md)


See [CHANGELOG.md](CHANGELOG.md) for changes and upgrade instructions.


See LICENSE.txt for further details.

*Note that all licence references and agreements mentioned in the Milia README section above are relevant to that project's source code only.