How to Implement Pagination in Ruby on Rails?

Pagination in Ruby on Rails is the process of dividing a large amount of material into smaller, easier-to-manage pages or chunks. This is frequently used in web applications to provide data in a more readable style, which enhances the user experience.

Ruby on Rails provides built-in techniques and gems for implementing pagination. 'will_paginate' is one of the most widely used gems for pagination, although there are other options as well, such as 'pagy' and 'kaminari'.

Using 'limit' and 'offset' Methods

You can implement pagination in Ruby on Rails manually without using methods like 'will_paginate'. Active Record is an ORM(Object-Relational Mapping) library that provides a set of methods and techniques to interact with databases using classes. We can use the 'limit' and 'offset' methods provided by Active Record.

Step 1: Create a demo project using the command below. It will create a project named 'railsapp' in the current directory. Then use the second command to get into your project directory.

rails new railsapp

cd railsapp

Step 2: Now, we will create a controller and view using the following command. This command creates a controller file named 'posts_controller.rb' in ‘app/controllers’ and its view file 'index.html.erb' in ‘app/views/home’. This command also creates a route file 'config/routes.rb'.

rails generate controller Posts index

Step 3: Next, we will create a 'Post' model which will have attributes as 'title' and 'content'.

rails generate model Post title:string content:text

Step 4: We will run the migration to create the table in our database. Run the following command in terminal. This will execute the migration file and create a posts table in our database with columns for title and content.

rails db:migrate

Step 5: Open 'db/seeds.rb' and fill example data. This code will create 5 posts with title and content.

# Generate example posts
5.times do |i|
    Post.create(title: "GeeksforGeeks Post #{i+1}", content: "This is content for post #{i+1}")
  end

Then run this command in terminal.

rails db:seed

Step 6: Now, we will implement pagination, for that open 'app/controllers/posts_controller.rb' and write the below code.

class PostsController < ApplicationController
  def index
    page = params[:page].to_i || 1
    @per_page = 2  # Number of records per page
    offset = (page - 1) * @per_page
    @posts = Post.limit(@per_page).offset(offset)
  end
end

Explanation:

• In this code, the first line retrieves the current page number from the URL parameters.
• It converts the page number to an integer using '.to_i'.
• If the page parameter is not present or evaluates to nil, it defaults to 1.
• Then we have defined that there will be 2 posts/records per page.
• The offset method determines how many posts to skip in the database query based on the current page number and the number of records per page.
• For example, on second page offset = (2 - 1) * 2 = 2, so the first two post will be skipped, since they already fetched on first page.

Step 7: Open 'app/views/posts/index.html.erb' and write the below code. It will display the content from database and creates Previous and Next buttons using 'link_to' method.

<% @posts.each do |post| %>
    <div>
      <h2><%= post.title %></h2>
      <p><%= post.content %></p>
    </div>
  <% end %>
  
  <% if params[:page].to_i > 1 %>
    <%= link_to "Previous", root_path(page: params[:page].to_i - 1) %>
  <% end %>
  
  <% if @posts.size == @per_page %>
    <%= link_to "Next", root_path(page: params[:page].to_i + 1) %>
  <% end %>
  

Step 8: Now, set the index page as root by changing the 'config/routes.rb' as mentioned below in code.

Rails.application.routes.draw do
  root 'posts#index'
end

Now, run the server using this command in terminal.

rails server

Output:

Using 'will_paginate' Gem

Gems are packages of code in Ruby, similar to libraries or plugins in other programming languages. A Gemfile is a configuration file used in Ruby on Rails applications, to specify the gems and their versions that the project depends on. The file is typically named as 'Gemfile'. We can implement pagination with 'will_paginate' gem, which is quite easier then doing manually.

Follow till Step 5 mentioned in previous method for creating Rails project and example database.

Step 1: Add the 'will_paginate' gem to your gemfile using this line. It specifies the gem name and its version.

Run the below command to install the gems.

bundle install

Step 2: Now, edit the 'app/controllers/posts_controller.rb' to add the pagination code using the 'paginate()' method provided by 'will_paginate' gem.

class PostsController < ApplicationController
  def index
    @posts = Post.paginate(page: params[:page], per_page: 2)
  end
end

Step 3: Open 'app/views/posts/index.html.erb' and add the below code to display the posts in database on webpage. The button for navigating will be created automatically since we are using 'will_paginate' gem.

<% @posts.each do |post| %>
  <div>
    <h2><%= post.title %></h2>
    <p><%= post.content %></p>
  </div>
<% end %>

<%= will_paginate @posts %>

Step 4: Edit the 'config/routes.rb' to make the index as root page and run the server using 'rails server' command.

Rails.application.routes.draw do
  root 'posts#index'
end

Output: