Lets suppose we have articles listing page and we need to show the 10 article per page. So there are we can use 'will_paginate' gem to divide the articles in number of pages.

There are the following steps to integrate the 'will_paginate' gem in our application

Add will_paginate gem in our Gemfile

gem 'will_paginate', '~> 3.0'

Then run command on rails console to install the gem

bundle install

After that we modify the controller for pagination like...

class ArticlesController < ApplicationController

  def index
     @articles = Article.paginate(:page => params[:page], :per_page => 5)
   end
end

page – This is query string parameter decided to which records are to be fetched.

per_page – This is number of record that we want to fetch per page

Modify index.html.erb to display pagination link

%= will_paginate(@articles,:previous_label => "«", :next_label =>"»") %>

previous_label - default: “« Previous”

This params used to display the pagination link for previous label, default link is “« Previous”

next_label - default: “Next »” This params used to display the pagination link for next label, default link is “« Previous”

There are lots of optional params which is passed to HTML attributes for displaying the pagination. If we want to displaying a message containing number of displayed vs. total entries. Add following code after pagination link on the index page .

<%= page_entries_info @article %>

It displaying message like...

Displaying Article 1 - 5 of 7 in total

We can also set per_page params into article.rb model instead of article controller

class Article < ActiveRecord::Base
    has_many :comments
	validates :title, presence: true, length: { minimum: 5 }
	self.per_page = 5
end

And also modify the article controller like...

class ArticlesController < ApplicationController

   def index
      #@articles = Article.paginate(:page => params[:page], :per_page => 5)
       @articles = Article.paginate(:page => params[:page])
   end
end

We can also set the per_page params globally using code like

WillPaginate.per_page = 10