We have been discussing refactoring in our previous posts. Next to our refactoring pattern, we will discuss few gems that can be used to improve our coding style.

In my last post i explained form objects pattern. Form objects are nothing but a replacement of your model object for form. Controllers are meant to receive request and provide result to the views. We can extract the form create/update functionality from controller and abstract it in a form object class.

Benefits of form object pattern are:

1. It abstract the functionality in a class which is concerned about that particular functionality only as stated by SRP (single responsibility principle).
2. Extract validations out of models that may not be necessary.
3. Reduces complexity in saving associated records (multiple model form).

For this tutorial we will look in to Reform gem which helps to create form objects. It maintains validations for one or multiple models, where a model can be any kind of Ruby object. Add reform gem to gemfile and bundle install.

copytext

gem "reform"

gem "reform"

Lets see an example:
 

copytext

class Author < ActiveRecord::Base
  has_many :books
end
 
 

class Author < ActiveRecord::Base
  has_many :books
end

copytext

class Books < ActiveRecord::Base
  belongs_to :author
end
 
 

class Books < ActiveRecord::Base
  belongs_to :author
end

We create a form object class that inherits from Reform::Form. We define attributes with property and validations in the class. Reform provides support for nested objects. As we have books association in our Author model. We can define this association in our form class with collection keyword.

 

copytext

class AuthorCreateForm < Reform::Form
  property :name
  validates :name, presence: true
 
  collection :books do
    property :name
    property :description
    property :publish_on
    validates :name, presence: true
  end
end

class AuthorCreateForm < Reform::Form
  property :name
  validates :name, presence: true

  collection :books do
    property :name
    property :description
    property :publish_on
    validates :name, presence: true
  end
end

Now in our controller we can use this:

copytext

class AuthorsController
  def new
    @form = AuthorCreateForm.new(Author.new)
  end
 
  def create
    @form = AuthorCreateForm.new(Author.new)
    if @form.validate(params[:author])
      @form.save
    else
      # handle validation errors.
    end
  end
end

class AuthorsController
  def new
    @form = AuthorCreateForm.new(Author.new)
  end

  def create
    @form = AuthorCreateForm.new(Author.new)
    if @form.validate(params[:author])
      @form.save
    else
      # handle validation errors.
    end
  end
end

Note: The #validate method first updates the values of the form. However, the model object does not save. It then runs validation. The values are saved only after #save or #sync operation are called on form object.

Passing this form object in our view:

copytext

= form_for @form do |f|
  = f.input :name
 
= f.fields_for :books do |a|
    = a.text_field :name
 
......

= form_for @form do |f|
  = f.input :name

= f.fields_for :books do |a|
    = a.text_field :name

......

NOTE: The save method on the form object will call #save on the model and nested models.

Conclusion:

Isn't that nice, we have extracted the functionality from controller in separate class. Our controllers are now more clean and skinny. Also our controller no longer deals with create/update logic.

You may use simple ruby class or Reform gem for form objects. Form objects pattern is useful with complex nested model forms. Reform provides us neat ways to define fields and associations.

For more details and options on reform gem please visit https://github.com/apotonick/reform