# 3 helpful methods in Rails console
Recently, I start reading [Practicing Rails](https://www.justinweiss.com/practicing-rails/). I love the main point in chapter 1: **Rails console is a good place to experiment with our ideas**.
There are 3 tips to explore ideas through the Rails console I learned from Practicing Rails.
### 1\. Use app object.
Who is `app`?
```ruby
$ app.class
#=> ActionDispatch::Integration::Session
# That means
app = ActionDispatch::Integration::Session.new(Rails.application)
```
According to the [source code]($ app.class #=> ActionDispatch::Integration::Session # That means app = ActionDispatch::Integration::Session.new(Rails.application)),
> An instance of this class represents a set of requests and responses performed sequentially by a test process.
And `ActionDispatch::Integration::Session` class includes the `ActionDispatch::Integration::RequestHelpers`. (Read more about [this module](https://github.com/rails/rails/blob/89361447e1491c8a756e46e94df70d82595d1534/actionpack/lib/action_dispatch/testing/integration.rb#L12))
So, we can use `app` to perform HTTP requests:
```ruby
$ app.get('http://localhost:3000/articles/1')
# Started GET "/articles/1" for 127.0.0.1 at 2021-07-07 15:14:08 +0800
# Processing by ArticlesController#show as HTML
# Parameters: {"id"=>"1"}
# Article Load (0.6ms) SELECT "articles".* FROM "articles" WHERE "articles"."id" = $1 LIMIT $2 [["id", 1], ["LIMIT", 1]]
# Rendering articles/show.html.erb within layouts/application
# Rendered articles/show.html.erb within layouts/application (Duration: 2.7ms | Allocations: 344)
# Rendered layouts/_header.html.erb (Duration: 0.4ms | Allocations: 145)
# Rendered layouts/_footer.html.erb (Duration: 0.5ms | Allocations: 91)
# Completed 200 OK in 17ms (Views: 13.3ms | ActiveRecord: 0.6ms | Allocations: 4199)
#=> 200
$ puts app.response.body.first(200)
#
#
#
# Lynn's Blog
# Hello world!"
```
If you find out that you get the `undefined method` error message when trying to call a custom `helper`. It might mean the module hasn't been included.
```ruby
$ helper.your_custom_helper_method
#=> NoMethodError: undefined method `your_custom_helper_method' for #
```
It's good timing to check `config/application.rb`, if the setting below is `false`.
```plaintext
config.action_controller.include_all_helpers = false
```
If you just want to check the return value of this custom helper method and don't want to change the setting above, we can include this helper module first:
```ruby
$ include Admin::ProjectsHelper
#=> Object < BasicObject
$ helper.your_custom_helper_method
#=> 'hi, how are you?'
```
---
### 3\. Use a special variable `_`.
The result of the last line we ran in the console is automatically saved in a variable named `_`.
For example,
```ruby
$ Article.new
#=> #
$ _
#=> #
# Assume `title` attribute cannot be blank
$ _.valid?
#=> false
$ _
#=> false
$ _.errors.messages
#=> Traceback (most recent call last):
# 2: from (irb):46
# 1: from (irb):47:in `rescue in irb_binding'
# NoMethodError (undefined method `errors' for #)
```
Next time, if we forget to assign a variable, we can just pick it up to use. :P
---
### Reference
* [https://www.justinweiss.com/practicing-rails/](https://www.justinweiss.com/practicing-rails/)
* [https://github.com/rails/rails/blob/89361447e1491c8a756e46e94df70d82595d1534/actionpack/lib/action\_dispatch/testing/integration.rb](https://github.com/rails/rails/blob/89361447e1491c8a756e46e94df70d82595d1534/actionpack/lib/action_dispatch/testing/integration.rb)