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If you need a simpler way to handle complex logic in your existing controller, you can use the Granite action by calling it in the controller action:

class MoviesController < ApplicationController
  # ...
  # Regular controller definition
  # ...
  def create
    BA::Movies::Create.with(performer: current_user).new(some_params).perform!
  # ...

However, this code can quickly become repetitive, so it's recommended to use projectors instead.

Projectors are mainly used to avoid duplicating code in controller actions and decorator methods. They enable business actions to be rendered into a user interface more easily.


A projector file has two parts:

  1. Decorator part is the projector class itself.

  2. Controller part is a nested class defined implicitly and accessible via TestProjector.controller_class.

For example:

class TestProjector < Granite::Projector

To mount projectors into actions and routes, you can use the projector method. It's possible to mount multiple projectors onto one action (e.g., if we need to execute a business action through a standard confirmation dialog or inline editing) or to have one projector mounted by several actions:

class Action < Granite::Action
  projector :test

  # Alternatively, you can specify a custom name:
  # projector :main, class_name: 'TestProjector'

When a projector is mounted onto an action, an inherited projector and a controller class are created:

pry(main)> Action.test
=> Action::TestProjector

pry(main)> Action.test.controller_class
=> Action::TestController

pry(main)> Action.test.action_class
=> Action(no attributes)

pry(main)> Action.test.controller_class.action_class
=> Action(no attributes)

To mount projectors onto routes, you need to specify a path to the projector as a string. If a business action has multiple projectors, each of them must be mounted separately in the routes. If an action doesn't have a subject, it should be mounted explicitly inside the collection block:

When you call granite in the routes, every controller of every mounted projector for the specified action is taken, and its controller actions are mounted onto the routes. You can also mount specific projectors.

Projectors can only be mounted inside a resource, and they are mounted on :member if they have a subject and on :collection otherwise:

Application.routes.draw do
  resources :users, only: [:index] do
    collection do
      granite 'create#my_projector'

    granite 'remove#my_projector'

When you mount a projector onto a route, the route will be defined by the resources block and the string provided. The Granite action and projector will be inferred by the parameter, which is split by the # character.

For instance, in the previous code block, the route /users/create/:projector_action is created, where the action is Create and the projector is MyProjector.

Next code block shows how the :projector_action refers to the projector controller action (baz and bar):

class FooProjector < Granite::Projector
  get :baz, as: '' do
    # ...

  get :bar do
    render json: { cats: 'nice' }

class Action < Granite::Action
  projector :foo

# config/routes.rb
# ...
resources :bunnies do
  granite 'action#foo'

In this context, the route /bunnies/action/bar corresponds to the bar action in the FooProjector, and /bunnies/action leads to the baz action in the same FooProjector.

Usually, projectors are mounted under /:action/:projector_action, where :action is the name of the BA, and :projector_action is mapped to the projector controller action.

Please note that if you have multiple projectors for the same action, they might use the same routes. To avoid conflicts between projectors, it's recommended to mount the second projector with projector_prefix: true. This will mount the projector under /:projector_:action/:projector_action instead of /:action/:projector_action. The same goes for the path helper method, which will be projector_action_subject_path instead of action_subject_path.

You can also customize the mount path using path: '/my_custom_path', as: :my_custom_action.

It's also possible to restrict the HTTP verbs for actions using via: :post (or :get, or any valid HTTP-action).

Lastly, you can access the projector instance from the action instance using the projector name:

=> #<Action::TestProjector:0x007f98bde9ac98 @action=#<Action (no attributes)>>

=> #<Action (no attributes)>

I18n projectors lookup

In Granite actions, there are special I18n rules that apply to projectors. When the I18n identifier is prefixed with a dot (t('.foobar')), translations are looked up in the following order:{granite_action_name}.#{granite_projector_name}.#{view_name}.foobar{granite_action_name}.#{granite_projector_name}.foobar

Decorator part

Since projectors behave like decorators, you can define helpers at the projector instance level. For example:

class TestProjector < Granite::Projector
  def link
    h.link_to action.subject.full_name, action.subject

class Action < Granite::Action
  projector :test
  subject :user

In your application, you can call this helper method like this:
# => "<a href=\"/user/112014\">Sebastián López Alfonso</a>"

This will generate a link to the User object's page with the user's full name as the link text. The link method is defined in the TestProjector and is called on the test projector instance that is associated with the Action object. The h helper method is provided by the projector instance and allows you to use Rails view helpers in your projector methods.

Controller part

The primary role of a controller is to serve actions, but in order to automatically detect controller actions and dispatch requests to them, we need a small DSL. Here's an example:

class TestProjector < Granite::Projector
  get :help do
    # render a view that shows help

  get :form, as: '' do
    # render a form. This is a default `get` action for this controller

  post :perform, as: '' do
    # process the form. This is a default `post` action for this controller

The first part of this code is the verb definition, which can be any REST verb. The second part is the mount point name to create a beautiful URL. You can set it using the :as option, and it's recommended to set it to an empty string so that the actual controller action isn't part of the URL.

For example, if you mounted the BA::Company::Create business action that had a projector with a perform controller action, the default path to the action would be create/perform. By adding as: '' to the perform action definition, you can change the path to create.

Note that the provided code defines methods called help, form, and perform in the controller_class. Also, keep in mind that calling render inside those blocks doesn't implicitly render the view within the application layout. To do so, you need to pass layout: 'application' to the render call.


The Granite::Controller is a subclass of ActionController::Base by default. However, it can be customized by changing the base_controller attribute in the Granite module's initializer. For example, to change the base controller to ApplicationController, you can do the following:

Granite.tap do |m|
  m.base_controller = 'ApplicationController'

In order to set the performer for Granite actions, you can implement the projector_performer method. For example, if you want to use the current_user method as the performer for all Granite actions, you can do the following:

def projector_performer

It's worth noting that Granite::Controller can be further customized after running the rails generate granite:install_controller command. The original controller will be installed in app/controllers/granite/controller.rb, which can be modified to fit your specific needs.

Handling policy exception

When an action's policies are not satisfied, Granite raises a Granite::Action::NotAllowedError exception. To handle this exception in the base_controller_class, you can use the rescue_from method like this:

class ApplicationController < ActionController::Base
  rescue_from Granite::Action::NotAllowedError do |exception|
    # Handle the exception

Inside the block, you can define how to handle the exception, for example by rendering an error page or redirecting the user to a different page.

Extending projectors

To provide more flexibility in customizing projectors, Granite allows passing a block to the projector declaration when mounting to business actions. This block can be used to configure the projector or even extend its controller class.

Here's an example:

class Action < Granite::Action
  projector :test do
    controller_class.before_action { ... }

    def link_class

In this example, the before_action hook is added to the controller class and a new method link_class is defined. While using a block to modify projectors is useful for small changes, it's often preferable to derive a new projector from a standard one for more significant modifications.


Views for projectors are used in the same way as views for usual controllers but are stored and inherited differently. Basic views for projectors are stored in apq/projectors/#{projector_name} directory.

If you need to redefine a specific template for a particular action, you can do so by placing the template in apq/actions/ba/#{action_name}/#{projector_name} for BA::ActionName.projector_name projector.