Rails Tricks Issue 2: Console Tricks

Hi, this is Greg with the second issue of Rails Tricks!

This week, I want to share a few Rails console tricks I use regularly. The first one is the _ command, which always holds the return value of the last evaluated command in IRB, which is the default for Rails` console. For instance, if you run an Active Record query to find a record, then you realize that you want to keep the result around, you can easily assign it to a variable:

irb(main):001:0> User.find_by(email: 'looking_for_you@gmail.com')
=>
#<User:0x00007f4b0fa3e150 ...
...
irb(main):002:0> user = _
=>
#<User:0x00007f4b0fa3e150 ...
...

Another thing I regularly do is, look up the definition of methods or the location of their definition. This comes in handy when you are debugging an issue and can be helpful to see what a method actually does or where it is defined. Because maybe a gem overrides it, and that causes unexpected behavior. In a Rails console, to see the definition, you can use Object.method(:name).source:

irb(main):009:0> puts User.method(:all).source
        def all
          scope = current_scope

          if scope
            if self == scope.klass
              scope.clone
            else
              relation.merge!(scope)
            end
          else
            default_scoped
          end
        end
=> nil

And if you want to verify that all is defined in Active Record and nothing overrides it in your application, you can check the location of the definition:

irb(main):010:0> puts User.method(:all).source_location
/home/gregmolnar/.rbenv/versions/3.2.0/lib/ruby/gems/3.2.0/gems/activerecord-7.0.4.2/lib/active_record/scoping/named.rb
22
=> nil

The source method is actually added by a gem called method_source, which was part of Rails between 7.1, but it will be removed with that release, so if you still want to be able to see the definition of methods in your console, you will need to add that gem to your Gemfile.

The next thing I want to share is the --sandbox option. If you pass this option when you start your console, every database modification will be rolled back on exit. This can be useful when you are debugging something in production, and you want to make sure you are not messing up something accidentally.

You can also read the documentation of Ruby classes inside the console by typing help('String') for instance.

And the final thing is to have some fun! Type IRB.send(:easter_egg, :dancing) or IRB.send(:easter_egg, :logo) in your IRB session and enjoy the result! You can exit by pressing CTRL+C.

P.S.: I just came across this blog post recently from Jemma about the measure command in IRB: https://jemma.dev/blog/irb-measure. I haven’t used this one yet, but probably will in the future.

This week I have a special guest trick!

# app/models/current.rb
class Current < ActiveSupport::CurrentAttributes
  attribute :account, :user
end

# app/controllers/concerns/authentication.rb
module Authentication
  extend ActiveSupport::Concern

  included do
    before_action :set_current
  end

  def set_current
    Current.user = current_user
    Current.account = user.account
  end
end

# config/initializers/avo.rb
Rails.configuration.to_prepare do
  Avo::ApplicationController.include Authentication
end

# app/avo/concerns/field_extensions.rb
module FieldExtensions
  # Include all helpers
  helper_names = ActionController::Base.all_helpers_from_path Rails.root.join("app", "helpers")
  helpers = ActionController::Base.modules_for_helpers helper_names

  helpers.each do |helper|
    send(:include, helper)
  end
end

# config/initializers/avo.rb
Rails.configuration.to_prepare do
  Avo::Fields::BaseField.include FieldExtensions
end

That’s it for this week, see you next time!

Greg