ActionArgs

Controller action arguments parameterizer for Rails 3 and 4

What is this?

ActionArgs 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, Merbish.

The Controllers

Having the following controller code:

class HogeController < ApplicationController
  def fuga(piyo)
    render :text => piyo
  end
end

Hitting "/hoge/fuga?piyo=foo" will call fuga('foo') and output 'foo'. This allows you to explicitly state which members of the params Hash are used in your controller actions,

StrongParameters

ActionArgs plays very nice with Rails 4 StrongParameters.

Required Parameters

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

In this show action, ActionArgs 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

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

StrongParameters - permit

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 white-listing

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

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

  # the given `user` parameter would be automatically permitted by ActionArgs
  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
  # white-lists User model's attributes
  permits :name, :age, model_name: 'User'
end

The Scaffold Generator

ActionArgs 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:

# coding: utf-8

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 action: 'new'
    end
  end

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

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

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

    redirect_to users_url
  end
end

You may notice that

There are no globalish params referrence
It's quite easy to comprehend what's the actual input value for each action
You may write the unit test code as if the actions are just normal Ruby methods

Supported versions

Ruby 1.9.2, 1.9.3, 2.0.0, 2.1.0 (trunk), JRuby & Rubinius with 1.9 mode
Rails 3.0.x, 3.1.x, 3.2.x, 4.0 (edge)

Installation

Put this line in your Gemfile:

gem 'action_args'

Then bundle:

% bundle

Notes

Plain Old Action Methods

Of courese you still can use both Merbish 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.