【Rails】What's the helper and partial?

Introduction

Hello.
I live in the U.S. and am studying programming by myself.
Recently, I'm studying Ruby on Rails with Rails Tutorial and I found that the function of helper and partial is to do DRY.
Today I'd like to explain what this function difference from.

Helper

Helper defines the module of the Ruby and it's the function used to abstract the logic with view and reuse.
It generally defines application_helper.rb and you can use it on all views in Rails.

Definition example

# app/helpers/application_helper.rb
module ApplicationHelper
  def full_title(page_title ='')
    base_title ="Rubyon RailsTutorial SampleApp"
    if page_title.empty?
      base_title
    else
      "#{page_title}| #{base_title}"
    end
  end
end

How to call

<!-- app/views/layouts/application.html.erb -->
<title><%= full_title(yield(:title)) %></title>

Range of adapting

• The method that was defined in application_helper.rb is possible to use on all views in Rails.
• If you'd like to use the controller you want to use, you have to define it at the helper file of this controller.

---

Partial

summary

Partial is the function used to extract a part of HTML/ERB and reuse it.
It saves as the file name used underline like _header.html.erb.

Case of Partial

• To reuse the layout like header, footer and sidebar
• Formalized factors used on another views.

Definition example

<!-- app/views/shared/_footer.html.erb -->
<footer>
  <p>© 2025 My Application</p>
</footer>

How to call

<!-- app/views/layouts/application.html.erb -->
<%= render 'shared/footer' %>

Range of adapting

• You can use every view files with using render command.
• You can use it from another controller of view if you write the file path clearly.

Comparison chart

Feature	Helper	Partial
Range of adapting	everywhere	Depend on the file path
Purpose of reusing	To abstract the logic	To abstract HTML/ERB
The file place	app/helpers/	app/views/
How to call	As the method (<%= helper_method %>)	Render (<%= render 'partial' %>)

Finally

Rails helpers and partials each serve different purposes, and by using them appropriately, you can improve your application's maintainability. Writing an article about something you only had a vague understanding of can help clarify their distinct differences. Since I'm currently learning Rails, I'll write another article if I come across anything new.