action_args

Controller action arguments parameterizer for Rails

What Is This?

action_args is a Rails plugin that extends your controller action methods to allow you to specify arguments of interest in the method definition for any action. - in short, this makes your Rails controller Merb-ish.

The Controllers

Having the following controller code:

class UsersController < ApplicationController
  def show(id)
    @user = User.find id
  end
end

When a request visits "/users/777", it calls UsersController#show passing 777 as the method parameter. This allows you to explicitly state the most important API for the action -- which members of the params Hash are used in your controller actions -- in a perfectly natural Ruby way!

Method Parameter Types in Ruby, and How action_args Handles Parameters

Required Parameters (:req)

Method parameters that you specify are required. If a key of the same name does not exist in the params Hash, ActionContrller::BadRequest is raised.

In this show action, action_args will require that id parameter is provided.

class UsersController < ApplicationController
  # the `id` parameter is mandatory
  def show(id)
    @user = User.find id
  end
end

Optional Parameters (:opt)

Default parameter values are assigned in the standard way. Parameters with a default value will not require a matching item in the params Hash.

class UsersController < ApplicationController
  # the `page` parameter is optional
  def index(page = nil)
    @users = User.page(page).per(50)
  end
end

Keyword Argument (:key)

If you think this Ruby 2.0 syntax reads better, you can choose this style for defining your action methods. This just works in the same way as :opt here.

class UsersController < ApplicationController
  # the `page` parameter is optional
  def index(page: nil)
    @users = User.page(page).per(50)
  end
end

Required Keyword Argument (:keyreq)

:keyreq is the required version of :key, which was introduced in Ruby 2.1. You can use this syntax instead of :req.

class CommentsController < ApplicationController
  def create(post_id:, comment:)
    post = Post.find post_id
    if post.create comment
      ...
  end
end

StrongParameters - permit

action_args plays very nice with Rails 4 StrongParameters.

Inline declaration

Hashes simply respond to the StrongParameters' permit method.

class UsersController < ApplicationController
  def create(user)
    @user = User.new(user.permit(:name, :age))
    ...
  end
end

Declarative allow-listing

action_args also provides a declarative permits method for controller classes. Use this to keep your permit calls DRY in a comprehensible way.

class UsersController < ApplicationController
  # allow-lists User model's attributes
  permits :name, :age

  # the given `user` parameter would be automatically permitted by action_args
  def create(user)
    @user = User.new(user)
  end
end

By default, action_args deduces the target model name from the controller name. For example, the permits call in UsersController expects the model name to be User. If this is not the case, you can specify the :model_name option:

class MembersController < ApplicationController
  # allow-lists User model's attributes
  permits :name, :age, model_name: 'User'
end

Filters

action_args works in filters, in the same way as it works in controller actions.

class UsersController < ApplicationController
  before_action :set_user, only: :show

  def show
  end

  # `params[:id]` will be dynamically assigned to the method parameter `id` here
  private def set_user(id)
    @user = User.find(id)
  end
end

The *_params Convention

For those who are familiar with the Rails scaffold's default naming style, you can add _params suffix to any of the parameter names in the method signatures. It just matches with the params name without _params.

For instance, these two actions both pass params[:user] as the method parameter.

# without _params
def create(user)
  @user = User.new(user)
  ...
end

# with _params
def create(user_params)
  @user = User.new(user_params)
  ...
end

This naming convention makes your controller code look much more compatible with the Rails' default scaffolded code, and so it may be actually super easy for you to manually migrate from the legacy scaffold controller to the action_args style.

The Scaffold Generator

action_args provides a custom scaffold controller generator that overwrites the default scaffold generator. Thus, by hitting the scaffold generator command like this:

% rails g scaffold user name age:integer email

The following elegant controller code will be generated:

class UsersController < ApplicationController
  permits :name, :age, :email

  # GET /users
  def index
    @users = User.all
  end

  # GET /users/1
  def show(id)
    @user = User.find(id)
  end

  # GET /users/new
  def new
    @user = User.new
  end

  # GET /users/1/edit
  def edit(id)
    @user = User.find(id)
  end

  # POST /users
  def create(user)
    @user = User.new(user)

    if @user.save
      redirect_to @user, notice: 'User was successfully created.'
    else
      render :new
    end
  end

  # PUT /users/1
  def update(id, user)
    @user = User.find(id)

    if @user.update(user)
      redirect_to @user, notice: 'User was successfully updated.'
    else
      render :edit
    end
  end

  # DELETE /users/1
  def destroy(id)
    @user = User.find(id)
    @user.destroy

    redirect_to users_url, notice: 'User was successfully destroyed.'
  end
end

You may notice that

There are no global-ish params reference
It's quite easy to comprehend what's the actual input value for each action
You may be able to write the unit test code without mocking params as if the actions are just normal Ruby methods

Supported Versions

Ruby 2.0.0, 2.1.x, 2.2.x, 2.3.x, 2.4.x, 2.5.x, 2.6.x, 2.7.x, 3.0.x, 3.1.x, 3.2.x, 3.3 (trunk), JRuby, & Rubinius with 2.0+ mode
Rails 4.1.x, 4.2.x, 5.0, 5.1, 5.2, 6.0, 6.1, 7.0, 7.1 (edge)

For Rails 4.0.x, please use Version 1.5.4.

Installation

Bundle the gem to your Rails app by putting this line in your Gemfile:

gem 'action_args'

Notes

Plain Old Action Methods

Of course you still can use both Merb-like style and plain old Rails style action methods even if this plugin is loaded. params parameter is still alive as well. That means, this plugin won't break any existing controller API.

Argument Naming Convention

Each action method parameter name corresponds to params key name. For example, the following beautifully written nested show action works perfectly (this might not be a very good example of effective querying, but that's another story).

Rails.application.routes.draw do
  resources :authors do
    resources :books
  end
end

class BooksController < ApplicationController
  # GET /authors/:author_id/books/:id
  def show(author_id, id)
    @book = Author.find(author_id).books.find(id)
  end
  ...
end

Default Parameter Values

You are of course able to specify default values for action parameters such as:

class BooksController < ApplicationController
  def index(author_id = nil, page = 1)
    ...
  end
end

However, due to some implementation reasons, the page variable will be actually defaulted to nil when page parameter was not given.

In order to provide default parameter values in perfect Ruby manner, we recommend you to use the Ruby 2.0 "keyword arguments" syntax instead.

class BooksController < ApplicationController
  def index(author_id: nil, page: 1)
    ...
  end
end

This way, the page parameter will be defaulted to 1 as everyone might expect.