ActionParameter

ActionParameter helps you move all your parameter's logic into it's own class. This way you'll keep your controllers dry and they would be easier to test.

Before

# app/controllers/users_controllers.rb
class UsersController < ActionController::Base
  def create
    User.create(user_params)
  end

  private
    def user_params
      params.require(:user).permit(:name, :age)
    end
end

After

# app/controllers/users_controllers.rb
class UsersController < ActionController::Base
  def create
    # It automatically deduces which Parameters class from Controller's name
    User.create(permitted_params.permit)
  end
end

# app/parameters/user_parameters.rb
class UserParameters < ActionParameter::Base
  def permit
    params.require(:user).permit(:name, :age)
  end
end

Install

ActionParameter works with Rails 3.0 onwards and Ruby 1.9.3 onwards. You can add it to your Gemfile with:

gem 'action_parameter'

Run the bundle command to install it.

Usage

####Generator

rails generate parameters [MODEL_NAME]

Will create app/parameters/[model_name]_parameters.rb.

####Controller Helpers

permitted_params: Returns an ActionParameter instance.

permitted_params(options={})

#####Options Hash

options - Hash with one valid key: :class.
options[:class] - Symbol value with the name of the Parameters class you want to use.

#####Example 1

# app/controllers/people_controllers.rb
class PeopleController < ActionController::Base
  def create
    Person.create(permitted_params.permit) # This will call to PersonParameters' permit method
  end
end

# app/parameters/person_parameters.rb
class PersonParameters < ActionParameter::Base
  def permit
    params.require(:person).permit(:name, :age)
  end
end

#####Example 2

# app/controllers/people_controllers.rb
class PeopleController < ActionController::Base
  def create
    Person.create(permitted_params(class: :user).sign_up) # This will call to UserParameters' sign_up method
  end
end

# app/parameters/user_parameters.rb
class UserParameters < ActionParameter::Base
  def sign_up
    params.require(:person).permit(:name, :age)
  end
end

####Parameter Class Helpers

#####Default Helpers

params: Returns params from the current controller request which instantiated the Parameter class.
controller_name: Returns the controller's name from which the Parameter class was instantiated.
action_name: Returns the action's name from the controller from which the Parameter class was instantiated.

#####Creating New Helpers

If you want to create new helper methods for your parameters class, just call locals method over permitted_params. Let say you want to make @current_user available for the UserParameter's class under the user method, then you'll need to use the locals method to tell the UserParameters class to create a new helper that returns @current_user.

permitted_params(class: :user).locals( user:           @current_user,
                                       another_helper: @value )

This will create user and another_helper methods and they will be available in UserParameters class.

#####Example

# app/controllers/users_controllers.rb
class UsersController < ActionController::Base
  def create
    User.create(permitted_params.locals(user: @current_user).permit) # This will call to UserParameters' permit method
  end
end

# app/parameters/user_parameters.rb
class UserParameters < ActionParameter::Base
  def permit
    if user.admin?
        params.require(:person).permit(:name, :age, :admin)
    else
        params.require(:person).permit(:name, :age)
    end
  end
end

RSpec

This example shows how to test using RSpec.

Theses tests require your test.rb configured to config.action_controller.action_on_unpermitted_parameters = :raise.

# spec/parameters/user_parameters_spec.rb
require "spec_helper"

describe UserParameters do
  describe ".permit" do
    describe "when permitted parameters" do
      it "returns the cleaned parameters" do
        user_params = { first_name: "John", last_name: "Doe" }
        params = ActionController::Parameters.new(user: user_params)

        permitted_params = UserParameters.new(params).permit

        expect(permitted_params).to eq user_params.with_indifferent_access
      end
    end

    describe "when unpermitted parameters" do
      it "raises error" do
        user_params = { foo: "bar" }
        params = ActionController::Parameters.new(user: user_params)

        expect{ UserParameters.new(params).permit }.
          to raise_error(ActionController::UnpermittedParameters)
      end
    end
  end
end