Explore rails console with pry

Before we get started, let's integrate pry with our rails application. It's pretty simple, just add pry to the development group of your Gemfile, then bundle install.

gem 'pry-rails', group: :development

Then fire up your rails console, when we want to find out what's out there in Linux shell, we always ls, let's do it in pry:

[1] pry(main)> ls
Rails::ConsoleMethods#methods: app  controller  helper  new_session  reload!
self.methods: inspect  to_s
locals: _  __  _dir_  _ex_  _file_  _in_  _out_  _pry_  default_command_set

So, what's app?

Let's find out what's that app, just cd into it, yeah, you can do that in pry:

[2] pry(main)> cd app
[3] pry(#<ActionDispatch::Integration::Session>):1>

Notice how the pry prompt changes? After we cd into app, we'er now in ActionDispatch::Integration::Session directory, no, no, 'context'. Wow, the app method gives us an integration session instance just like we'er integration test Rails. That means we can call all the integration test helpers on app, such as generating routes:

>> topic_path Topic.first
=> "/topics/1"
# normally, we would call app.topic_path Topic.first, but
# since we'er 'inside app', we can eleminate that.

We can also make requests to out application directly in rails console:

>> get "/topics/1"
=> 200
>> response  # to get the response object
=> ...       # output suppressed for simplicity

Once again, normally we would call these methods on app. Another trick is, instead of copy paste last commands return value, we can reference it by _, so after we get the topic path, we can just get _ to make the requests. By default, pry will print out last command's return value, you may find it too verbose sometimes, To suppress the output, add a semicolon after the command: response;

Let's move on to the helper

[6] pry(#<ActionDispatch::Integration::Session>):1> cd ../helper
[7] pry(#<ActionView::Base>):1>

Now you should feel at home, all the helper methods you love are all here:

>> time_ago_in_words Topic.first.created_at
=> "1 day"
>> number_to_currency(8.88)
=> "$8.88"
# Remember, we'er in the helper context

As to more about helper, be sure to check about Nick Quaran's post Three quick Rails console tips

What about the controller

[10] pry(#<ActionView::Base>):1> cd ../controller
[11] pry(#<ApplicationController>):1> 

controller just returns a new ApplicationController instance, let's try get the params and flash out:

>> params
=> NoMethodError: undefined method `parameters' for nil:NilClass
>> flash
=> RuntimeError: ActionController::Base#flash delegated to request.flash, but request is nil

Oops! The problem is the app, helper, controller object is not hooked together, we have to do it mannually.

>> app.get '/'
=> 200
>> controller.request = app.request;
>> helper.controller = controller;
>> controller.flash
=> #<ActionDispatch::Flash::FlashHash:0xb5941b90 @discard=#<Set:{}>, @flashes={}, @now=nil>
>> helper.params
=> { "action" => "index", "controller" => "topics" }

reload! and new_session

reload! makes your code changes outside console available to current session. new_session returns a new instance of ActionDispatch::Integration::Session, app calls this method internally, here is the source code:

# File railties/lib/rails/console/app.rb, line 8
def app(create=false)
  @app_integration_instance = nil if create
  @app_integration_instance ||= new_session do |sess|
    sess.host! "www.example.com"