Ruby on Rails Debugging Debugging ruby-on-rails application with pry


pry is a powerful tool that can be used to debug any ruby application. Setting up a ruby-on-rails application with this gem is very easy and straightforward.


To start debugging your application with pry

  • Add gem 'pry' to the application's Gemfile and bundle it
group :development, :test do
  gem 'pry'
  • Navigate to the application's root directory on terminal console and run bundle install. You're all set to start using it anywhere on your application.


Using pry in your application is just including binding.pry on the breakpoints you want to inspect while debugging. You can add binding.pry breakpoints anywhere in your application that is interpreted by ruby interpreter (any app/controllers, app/models, app/views files)

i) Debugging a Controller


class UsersController < ApplicationController
  def show
    use_id = params[:id]
    // breakpoint to inspect if the action is receiving param as expected
    @user = User.find(user_id)
    respond_to do |format|

In this example, the rails server pauses with a pry console at the break-point when you try to visit a page routing to show action on UsersController. You can inspect params object and make ActiveRecord query on User model from that breakpoint

ii) Debugging a View


      %td ID
      %td email
      %td logged in ?          
        - binding.pry
        - if @user.logged_in?
          %p= "Logged in"
        - else
          %p= "Logged out"

In this example, the break-point pauses with pry console when the users/show page is pre-compiled in the rails server before sending it back to the client's browser. This break-point allows to debug correctness of @user.logged_in? when it is misbehaving.

ii) Debugging a Model


class User < ActiveRecord::Base    
  def full_name
    "#{self.first_name} #{self.last_name}"

In this example, the break-point can be used to debug User model's instance method full_name when this method is called from anywhere in the application.

In conclusion, pry is a powerful debugging tool for rails application with easy setup and straightforward debugging guideline. Give this a try.