Ruby on Rails 5+ Simple Contact Form

_error_messages.html.erb

<!-- If you do not used a shared error message across your app, paste this code in the 
app/views/contact/index.html.erb file in place of the <%= render 'shared/error_messages %> -->

<% if object.errors.any? %>
  <article class="message is-danger">
    <div class="message-header">
      The form contains <%= pluralize(object.errors.count, 'error') %>.
    </div>
    <div class="message-body">
      <ul>
        <% object.errors.full_messages.each do |msg| %>
          <li><%= msg %></li>
        <% end %>
      </ul>
    </div>
  </article>
<% end %>

contact.rb

# Generate a Contact model with the command. We skip the migration, as this implementation does not use Active Record:

# rails generate model contact --no-migration

# Update the model file as follows, adding validations to each field to require user to input them and using 
# regex to ensure a valid email address.

class Contact < MailForm::Base
  # Your whitelisted parameters
  attribute :name
  attribute :email
  attribute :message

  VALID_EMAIL_REGEX = /\A[\w+\-.]+@[a-z\d\-.]+\.[a-z]+\z/i
  validates :name, presence: true, length: { minimum: 3, maximum: 50 }
  validates :email, presence: true, length: { maximum: 255 }, format: { with: VALID_EMAIL_REGEX }
  validates :message, presence: true, length: { minimum: 10 }

  # Declare the e-mail headers. It accepts anything the mail method
  # in ActionMailer accepts.
  def headers
    {
      :subject => 'Contact from completed from your Website',
      :to => 'your@email.com', #add multiple addresses 
      :from => %("#{name}" <#{email}>)
    }
  end
end

contact_controller.rb

# Next, generate a Contact Controller to handle messages submitted, generate with `index` for the one view. 
# I  omit assets, helpers and stylesheets as I don't need them in my typical implementations. 
# Remove the flags if you wish to.

# rails generate controller Contact index --no-assets --no-stylesheets --no-helper

# We now update our controller to handle messages as follows, this is a simple contact form, 
# if the message is valid and sends, it will redirect the user to the home page and flash a message thanking 
# them for the message. If it fails, it re-renders the Contact page, alerts the user to the error
# and keeps their inputs. We also whitelist our message paramters:

# Update controller as follows:

class ContactController < ApplicationController
  def index
    @contact = Contact.new(params[:contact])
  end

  def create
    @contact = Contact.new(params[:contact])
    @contact.request = request
    if @contact.deliver
      redirect_to root_url
      flash[:success] = 'Thank you for your message! We will get back to you soon'
    else
      render :index
    end
  end

  private

    def contact_params
      params.require(:contact).permit(:name, :email, :message)
    end

end

Gemfile

# Add the Mail Form gem to your gemfile.

gem 'mail_form'

# Then run:
bundle install

index.html.erb

<!-- app/views/contact/index.html.erb

Updating the view, this has no styling, so you are on your own with that. We rely on the error message 
rendering for the rest of our App to keep our code nice and DRY. -->

<h1>Contact Us</h1>

<%= form_for @contact, url: contact_index_path do |f| %>
	<%= render 'shared/error_messages', object: f.object %>

	<%= f.label :name %>
	<%= f.text_field :name, required: true, type: 'text', placeholder: 'Your Name' %>

	<%= f.label :email %>
	<%= f.email_field :email, required: true, type: 'email', placeholder: 'Your Email Address' %>

	<%= f.label :message %>
	<%= f.text_area :message, rows: 8, cols: 40, required: true, class: 'textarea', placeholder: 'Your message to us' %>

	<%= f.submit 'Send Message' %>

<% end %>