Ruby on Rails - debugging application with pry in ruby on rails - ruby on rails tutorial - rails guides - rails tutorial - ruby rails

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

group :development, :test do
  gem 'pry'
end

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)

app/controllers/users_controller.rb

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

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

app/views/users/show.html.haml

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

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.

app/models/user.rb

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

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.