Cohabit

Cohabit adds comprehensive scoped multi-tenancy functionality to any application, simply set your options up in config/cohabit.rb using the DSL (inspired by capistrano).

This gem isn't really recommended for doing simple application wide scoping, for that I'd recommend https://github.com/wireframe/multitenant. Cohabit builds on what multitenant provides and allows you to define your own scoping strategies with the DSL for where more complexity is needed.

It provides (or it will):

Model scoping (duh)
Custom scoping strategies
Scope validations
Scope URL helpers
Rake task for importing single-tenanted databases into a multi-tenant one
Rake task for generating multi-tenanted scoped schema

Installation

Add this line to your application's Gemfile:

gem 'cohabit'

And then execute:

$ bundle

Or install it yourself as:

$ gem install cohabit

Usage

In its simplest form, using the basic scope (typical belongs_to assiciation scope):

# must have this line to use the included scopes
require 'basic'
scope [:foo, :bar], :basic

By default it assumes your tenant model is called tenant, if you wish to change this you can set it globally:

set :association, :organisation
scope [:foo, :bar], :basic

Or per scope with options:

scope [:foo, :bar], :basic, association: :organisation

Or you can specify options and other configuration settings in block form:

scope [:foo, :bar] do
  use_strategy: :basic
  set :association, :organisation
end

In your application, depending on how you determine the current tenant, you need to set Cohabit.current_tenant. If you're using subdomains, I would recommend writing some simple Rack middleware something like:

class TenantSetup
  def initialize(app)
    @app = app
  end

  def call(env)
    @request = Rack::Request.new(env)
    Cohabit.current_tenant = Tenant.find_by_subdomain!(get_subdomain)
    @app.call(env)
  end

  private
    def get_subdomain
      # Check request host isn't an IP.
      host = @request.host
      return nil unless !(host.nil? || /\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}$/.match(host))
      subdomain = host.split('.')[0..-3].first
      return subdomain unless subdomain == "www"
      return host.split('.')[0..-3][1]
    end
end

Alternatively, write a before_filter in the ApplicationController.

Strategies

This part is a WIP, but you can define your own strategies to be used. The following is the :basic strategy that comes by default:

strategy :basic do
  # simply gets evaluated in the models..
  model_eval do |_scope|
    # _scope var references the scope that uses the strategy,
    # so to access settings, like :association, use
    # _scope.settings[:association]. current_tenant is defined
    # as Cohabit.current_tenant.

    # add relationship
    belongs_to _scope.settings[:association]

    # get foreign key
    reflection = reflect_on_association _scope.settings[:association]

    # scope insertions
    before_create Proc.new {|m|
      return unless Cohabit.current_tenant
      m.send "#{_scope.settings[:association]}=".to_sym, Cohabit.current_tenant
    }

    # scope selects
    default_scope lambda {
      where(reflection.foreign_key => Cohabit.current_tenant) if Cohabit.current_tenant
    }
  end
end

You can define additional global vars in the Cohabit namespace, in your strategies, e.g.:

strategy :test do
  set :globals, [:current_view, :current_scope]
  # ...
end

# application_controller.rb
before_filter :set_scope
def set_scope
  Cohabit.current_scope = Cohabit.current_tenant.managed_clients
end

You can also nest strategies to DRY up your code a bit.

strategy :basic_tweaked do
  include_strategy :basic
  model_eval do |_scope|
    # ...
  end
end

Settings

Once I've implemented it, you'll be able to scope URL helpers, so for example if your tenant features in your URL like so:

# routes file
# ...
resources :tenants do
  resources :posts
  resources :foo
  resources :bar
end
# ...

Giving you the paths /tenant/1/posts/1 .. etc. You will be able to still call posts_path(@post), and when the setting is enabled it will expand that internally to tenants_posts_path(@post.tenant, @post).

Rake tasks

There are two rake tasks in the pipeline to make life a bit easier for anyone converting from multi-database architecture to a multi-tenant, single-database architecture:

Migrate DB or create new DB schema based on the scopes in a cohabit configuration file
Import a number of single-tenanted databases into the multi-tenanted equivalent

Todo

Still a WIP. Need to:

Work out how to integrate the url helper scopes as an option
Write the rake tasks
Add custom cohabit_unscoped (or similar) class method to models which removes all Cohabit default_scopes, before_creates, validation scopes, etc for that chain. (Possible? hmf)
Add a conditions option to include_strategy, like that of Rails routes perhaps

Contributing

Fork it
Create your feature branch (git checkout -b my-new-feature)
Commit your changes (git commit -am 'Add some feature')
Push to the branch (git push origin my-new-feature)
Create new Pull Request