Rails debug cheat sheet

gistfile1.md

Setup

Replace IRB with Pry (in your Gemfile) and Byebug with pry-byebug.

gem 'pry-rails', group: [:development, :test]
gem 'pry-byebug', group: [:development, :test]

Using PRY

Put pry somewhere in your code to start pry session

def my_method
  pry
  ...
end

Common commands

• Show method source

pry> $ object.method
# or class instance method
pry> $ Class#method  
# or class static method
pry> $ Class.method

• Show method docs

pry> ? object.method
# or class instance method
pry> ? Class#method  
# or class static method
pry> ? Class.method

• Show object methods and instance variables

pry> ls object
# or only public methods
pry> ls -m object
# or grep by name
pry> ls -G has_ object
# or instance variables
pry> ls -i object

• Move between objects

pry> cd user
pry(User):1> self
=> User
# switch back
pry(User):1> cd ..
# or switch to the top
pry(User):1> cd /

• Stop PRY session

# if you're in the top scope
pry> exit
# otherwise
pry> exit-all
# or
pry> !!!

Rails specific commands

• Show routes

pry> show-routes

• Show models info

pry> show-models
pry> show-model User
# or search model by attributes
pry> show-models -G password

• Show controller routes

pry> find-routes UsersController

Debugging with pry-byebug

• Start debug session

# somewhere in your code
binding.pry

• Navigation

# step into the next line/method
pry> step
# or step multiple times
pry> step 3

# step over to the next line/method
pry> next
# or
pry> next 2

# exit current stack frame
pry> finish

# move the stack frame up/down 
pry> up
pry> down
pry> up 3
pry> down 4

# continue to the next breakpoint
pry> continue
# or
pry> exit

• Breakpoints

# add breakpoint by the line number
pry> break /path/to/project/app/models/user.rb:22
# or by class and method name
pry> break User#admin?

# disable all breakpoints
pry> break --disable-all
# disable by number
pry> break -d 1
# enable by number
pry> break -e 1

# breakpoint with condition
pry> break User#my_method --condition 4 id == 2 # breaks only if id equals 2

Capybara helpers

• Save page as html

# Change output dir
Capybara.save_and_open_page_path = "./tmp/capybara"

# Add to your code to save current page state
save_page
# or save and open saved page in your browser
save_and_open_page

How to open saved page when using VM.

• Save page as image

save_screenshot('path/to/my.png')

• Pause test server and login to test session

# Setup Capybara server (somewhere in acceptance_helper)
Capybara.server_port = 3000 # or everything you want)
Capybara.server_host = "0.0.0.0" # to access server running within VM

# in your test code
pry # simply start PRY session

# and then open browser and login with current user credentials

Debugging js views

# view.erb.js
debugger;
$('.my-link').hide()
...