Acts As Tenant

Note: acts_as_tenant was introduced in this blog post.

This gem was born out of our own need for a fail-safe and out-of-the-way manner to add multi-tenancy to our Rails app through a shared database strategy, that integrates (near) seamless with Rails.

acts_as_tenant adds the ability to scope models to a tenant. Tenants are represented by a tenant model, such as Account. acts_as_tenant will help you set the current tenant on each request and ensures all 'tenant models' are always properly scoped to the current tenant: when viewing, searching and creating.

In addition, acts_as_tenant:

• sets the current tenant using the subdomain or allows you to pass in the current tenant yourself
• protects against various types of nastiness directed at circumventing the tenant scoping
• adds a method to validate uniqueness to a tenant, validates_uniqueness_to_tenant
• sets up a helper method containing the current tenant

Installation

acts_as_tenant will only work on Rails 3.1 and up. This is due to changes made to the handling of default_scope, an essential pillar of the gem.

To use it, add it to your Gemfile:

gem 'acts_as_tenant'

Getting started

There are two steps in adding multi-tenancy to your app with acts_as_tenant:

1. setting the current tenant and
2. scoping your models.

Setting the current tenant

There are three ways to set the current tenant: (1) by using the subdomain to lookup the current tenant, (2) by setting the current tenant in the controller, and (3) by setting the current tenant for a block.

Use the subdomain to lookup the current tenant

class ApplicationController < ActionController::Base
  set_current_tenant_by_subdomain(:account, :subdomain)
end

This tells acts_as_tenant to use the current subdomain to identify the current tenant. In addition, it tells acts_as_tenant that tenants are represented by the Account model and this model has a column named 'subdomain' which can be used to lookup the Account using the actual subdomain. If ommitted, the parameters will default to the values used above.

Setting the current tenant in a controller, manually

class ApplicationController < ActionController::Base
  set_current_tenant_through_filter
  before_filter :your_method_that_finds_the_current_tenant
  
  def your_method_that_finds_the_current_tenant
    current_account = Account.find_it
    set_current_tenant(current_account)
  end
end

Setting the current_tenant yourself, requires you to declare set_current_tenant_through_filter at the top of your application_controller to tell acts_as_tenant that you are going to use a before_filter to setup the current tenant. Next you should actually setup that before_filter to fetch the current tenant and pass it to acts_as_tenant by using set_current_tenant(current_tenant) in the before_filter.

Setting the current tenant for a block

ActsAsTenant.with_tenant(current_account) do
  # Current tenant is set for all code in this block
end

This approach is useful when running background processes for a specified tenant. For example, by putting this in your worker's run method, any code in this block will be scoped to the current tenant. All methods that set the current tenant are thread safe.

note: If the current tenant is not set by one of these methods, Acts_as_tenant will be unable to apply the proper scope to your models. So make sure you use one of the two methods to tell acts_as_tenant about the current tenant.

Require tenant to be set always

If you want to require the tenant to be set at all times, you can configure acts_as_tenant to raise an error when a query is made without a tenant available. See below under configuarion options.

Scoping your models

class Addaccounttousers < ActiveRecord::Migration
  def up
    add_column :users, :account_id, :integer
  end
end

class User < ActiveRecord::Base
  acts_as_tenant(:account)
end

acts_as_tenant requires each scoped model to have a column in its schema linking it to a tenant. Adding acts_as_tenant to your model declaration will scope that model to the current tenant BUT ONLY if a current tenant has been set.

Some examples to illustrate this behavior:

# This manually sets the current tenant for testing purposes. In your app this is handled by the gem.
ActsAsTenant.current_tenant = Account.find(3)   

# All searches are scoped by the tenant, the following searches will only return objects 
# where account_id == 3
Project.all =>  # all projects with account_id => 3
Project.tasks.all #  => all tasks with account_id => 3
 
# New objects are scoped to the current tenant
@project = Project.new(:name => 'big project')    # => <#Project id: nil, name: 'big project', :account_id: 3>

# It will not allow the creation of objects outside the current_tenant scope
@project.account_id = 2
@project.save                                     # => false
  
# It will not allow association with objects outside the current tenant scope
# Assuming the Project with ID: 2 does not belong to Account with ID: 3
@task = Task.new  # => <#Task id: nil, name: nil, project_id: nil, :account_id: 3>

Acts_as_tenant uses Rails' default_scope method to scope models. Rails 3.1 changed the way default_scope works in a good way. A user defined default_scope should integrate seamlessly with the one added by acts_as_tenant.

Validating attribute uniqueness

If you need to validate for uniqueness, chances are that you want to scope this validation to a tenant. You can do so by using:

validates_uniqueness_to_tenant :name, :email

All options available to Rails' own validates_uniqueness_of are also available to this method.

Configuration options

An initializer can be created to control (currently one) option in ActsAsTenant. Defaults are shown below with sample overrides following. In config/initializer/acts_as_tenant.rb:

ActsAsTenant.configure do |config|
  config.require_tenant = false # true
end

• config.require_tenant when set to true will raise an ActsAsTenant::NoTenant error whenever a query is made without a tenant set.

Note on testing

Whenever you set the current_tenant in your tests, either through integration tests or directly by calling ActsAsTenant.current_tenant = some_tenant, make sure to clean up the tenant after each test by calling ActsAsTenant.current_tenant = nil.

To Do

• Change the tests to Test::Unit so I can easily add some controller tests.

Bug reports & suggested improvements

If you have found a bug or want to suggest an improvement, please use our issue tracked at:

github.com/ErwinM/acts_as_tenant/issues

If you want to contribute, fork the project, code your improvements and make a pull request on Github. When doing so, please don't forget to add tests. If your contribution is fixing a bug it would be perfect if you could also submit a failing test, illustrating the issue.

Author & Credits

acts_as_tenant is written by Erwin Matthijssen.
Erwin is currently busy developing Roll Call.

This gem was inspired by Ryan Sonnek's Multitenant gem and its use of default_scope.

License

Copyright (c) 2011 Erwin Matthijssen, released under the MIT license