Rails Console Magic Tricks

Seven techniques to increase the developer experience during a Rails Console session. Please note that some of them will come from Ruby itself, and thus won’t be necessarily restricted to the console.

1. 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

2. 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"]

3. 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 Arrayone 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]

4. Finding out a method 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 specially 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]

5. Returning the source code of a method

While it is interesting to know the exactly location of a method, there are cases where 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

6. 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..."

7. 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, for instance, to interact with your application as a HTTP client would, and much more:

  • 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", ...

Have a trick of your own that you'd like to share? Leave a comment, I'd love to hear about it. Learned something new? Share this article and spread the word!