Rails Console Magic Tricks

In this article we are going to explore some techniques to enhance the experience of a Rails console session. Some of these will come from Ruby itself, and will also be also available in a plain IRB session.

Rolling Back After the End of a Session

It is possible to run the console in a mode called sandbox. In that mode, every change made to the database will be automatically rolled back when the session terminates:

$ rails console --sandbox

Retrieving the Previous Execution Value

The result of the immediately previous console execution can be retrieved and, as the example suggests, assigned to a local variable by calling the _:

>> Game.all.map(&:name)
=> ["zelda", "mario", "gta"]
>> names = _
=> ["zelda", "mario", "gta"]

Searching for Methods With grep

It is possible to find out the complete name of a method having only a part of it. By calling grep from Array, one can execute a handy search over the methods of a given object:

>> Game.first.methods.grep(/lumn/)
Game Load (0.8ms)  SELECT  "games".* FROM "games" ORDER BY "games"."id" ASC LIMIT $1  [["LIMIT", 1]]
=> [:column_for_attribute, :update_column, :update_columns]

Finding Out a Method’s Source Location

The source_location method from the Object class returns the full path of a method’s file definition, including the line where it was defined. It can be especially useful when exploring third-party libraries:

>> 'Luis Vasconcellos'.method(:inquiry).source_location
["/usr/local/bundle/gems/activesupport-5.2.1/lib/active_support/core_ext/string/inquiry.rb", 12]

Returning the Source Code of a Method

While it is interesting to know the exact location of a method, there are cases where it might be even better to output its source code directly to the console. This can be achieved by calling source from Object:

>> 'Luis Vasconcellos'.method(:inquiry).source.display
def inquiry
    ActiveSupport::StringInquirer.new(self)
  end
=> nil

The Helper Object

The console provides an object called helper, which can be used to directly access any view helper from a Rails application:

>> helper.truncate('Luis Vasconcellos', length: 9)
=> "Luis V..."

The App Object

The console also provides an interesting object called app, which is basically an instance of your application. With this object, it’s possible to interact with your application as an HTTP client would, among other interesting things.

Access to GET endpoints:

>> app.get('/')
Started GET "/" for 127.0.0.1 at 2018-08-25 22:46:52 +0000
   (0.5ms)  SELECT "schema_migrations"."version" FROM "schema_migrations" ORDER BY "schema_migrations"."version" ASC
Processing by HomeController#show as HTML
  Rendering home/show.html.erb within layouts/application
  Rendered home/show.html.erb within layouts/application (11417.2ms)
  Rendered shared/_menu.html.erb (3.6ms)
  Rendered shared/header/_autocomplete.html.erb (292.2ms)
  Rendered shared/_header.html.erb (312.9ms)
  Rendered shared/_footer.html.erb (3.7ms)
Completed 200 OK in 11957ms (Views: 11945.5ms | ActiveRecord: 0.0ms)
=> 200

Access to POST endpoints:

>> app.post('/games/zelda/wishlist_placements.js')
Started POST "/games/zelda/wishlist_placements.js" for 127.0.0.1 at 2018-08-25 23:03:21 +0000
Processing by OwnlistPlacementsController#create as JS
  Parameters: {"game_slug"=>"zelda"}
  Game Load (0.6ms)  SELECT  "games".* FROM "games" WHERE "games"."slug" = $1 LIMIT $2  [["slug", "zelda"], ["LIMIT", 1]]
  Rendering wishlist_placements/create.js.erb
  Rendered wishlist_placements/create.js.erb (194.8ms)
Completed 200 OK in 261ms (Views: 252.9ms | ActiveRecord: 0.6ms)
=> 200

Search for a _path helper from a Game route:

>> app.methods.grep(/_path/).grep(/game/)
=> [:search_games_path, :game_ownlist_placements_path, :game_ownlist_placement_path, :game_wishlist_placements_path, :game_wishlist_placement_path, :game_path]

Combining the previous tricks in a more useful way:

>> app.get(app.root_path)
Started GET "/" for 127.0.0.1 at 2018-08-26 02:27:40 +0000
Processing by HomeController#show as HTML
  Rendering home/show.html.erb within layouts/application
  Rendered home/show.html.erb within layouts/application (12550.2ms)
  Rendered shared/_menu.html.erb (3.8ms)
  Rendered shared/header/_autocomplete.html.erb (1.2ms)
  Rendered shared/_header.html.erb (28.0ms)
  Rendered shared/_footer.html.erb (3.8ms)
Completed 200 OK in 12835ms (Views: 12810.0ms | ActiveRecord: 0.0ms)
=> 200
>> app.body.response
=> "\n<!DOCTYPE html>\n<html>\n  <head>\n    <title> ...
>> app.cookies
=> #<Rack::Test::CookieJar:0x0000556ee95c33e0 @default_host="www.example.com", @cookies=[#<Rack::Test::Cookie:0x0000556eeb72b2d0 @default_host="www.example.com", ...

luis@home:~$