Changes to ActiveRecord::Dirty in Rails 5.2

A while ago I wrote a small post on how to manually mark an ActiveRecord model attribute as dirty. Since Rails 5.2 has some fundamental changes to ActiveRecord::Dirty.

Specifically, three methods have been deprecated and changed in 5.2. These are:

  • attribute_changed?
  • changes, and
  • previous_changes

Using these methods in a Rails 5.2 application will now result in the following message (or a variation of it) being outputted in your logs:

DEPRECATION WARNING: The behavior of `attribute_changed?` inside of after callbacks will be changing in the next version of Rails. The new return value will reflect the behavior of calling the method after `save` returned (e.g. the opposite of what it returns now). To maintain the current behavior, use `saved_change_to_attribute?` instead.

attribute_changed? and changed? remain the same when called within a before_save callback. But when used in an after callback there are new methods you should use instead, which the Rails Core Team believe should reduce code ambiguity of changed? before saving to the database: will_save_change_to_attribute? and has_changes_to_save?

In summary, if upgrading to Rails 5.2 and after modifying an object and after saving to the database, or within after_save:

  • attribute_changed? should now be saved_change_to_attribute?
  • changed? should now be saved_changes?
  • changes should now be saved_changes
  • previous_changes has no replacement, since the behavior for it changes.

And (optional; less ambiguity, more readable, but longer) after modifying an object and before saving to the database, or within before_save:

  • attribute_changed? should now be will_save_change_to_attribute?
  • changed? should now be has_changes_to_save?
  • changes should now be changes_to_save

“No route to host” error while trying to install RVM

In rare cases the gpg --keyserver can fail in the process of installing RVM on MacOS. Luckily, there is a command you can run to circumvent this problem. Try using this instead:

curl -sSL | gpg --import -

You should see in the results something like this:

  gpg: Total amount processed: 1 
gpg: imported: 1

Which should mean that everything has worked as expected. Now try following all the remaining commands, starting with this:

\curl -sSL | bash -s stable

Decorating Devise (current_user) with Draper

Devise is a wonderful and amazing gem to handle user authentication and provides a number of extremely useful utility helpers throughout your Rails application. Draper is an equally amazing gem, which provides a framework for using the decorator pattern in your Rails applications.

The model that encapsulates your User is usually one of the objects most in need of the decorator pattern, however, the current_user object provided by Devise returns the undecorated version of the user model. However, a simple method placed in your base ApplicationController class can solve this more elegantly that constantly calling current_user.decorate throughout your code:

def current_user   
UserDecorator.decorate(super) unless super.nil?

How to Log Which Line Initiated a Query in Rails

Create a file (something like) config/initializers/active_record_log_subscriber.rb

…and paste this into its contents:

module LogQuerySource
  def debug(*args, &block)
    return unless super

    backtrace = Rails.backtrace_cleaner.clean caller

    relevant_caller_line = backtrace.detect do |caller_line|

    if relevant_caller_line
      logger.debug("  ↳ #{ relevant_caller_line.sub("#{ Rails.root }/", '') }")
ActiveRecord::LogSubscriber.send :prepend, LogQuerySource

Now, whenever a line of code initiates a SQL query the line will be logged.  This greatly improves the ease of tracking down inefficiencies such as like N + 1 queries.

If you would like to learn more about exactly how this mix-in works and how the original author went about figuring out how to add it, you can read more about it here.


Commenting and Documentation in Ruby and Rails

It’s always been frustrating to me that Ruby and Rails don’t really have strong templated standards on how to best document your code. There are several options available and it can all be very confusing and unclear.

There is one template I’ve found works best and its super simple:

# Brief explanation of what the code does.
# * *Args* :
# - ++ ->
# * *Returns* :
# -
# * *Raises* :
# - ++ ->
def my_method


While there are many other perfectly good documentation libraries this has the benefits of being simple to remember, very easy to read in code, and compiles out super nicely using

rake doc:app

Example (strongly based off this post):

# This is an example method commented the way I 
# like. It sums the three arguments and returns 
# that value.
# Lorem ipsum dolor sit amet, consectetur adipising,
# do eiusmod tempor incididunt ut labore et dolore. 
# Ut enim ad minim veniam, quis nostrud exercit
# laboris nisi ut aliquip ex ea commodo consequat.
# * *Args* :
#   - +apples+ -> the number of apples
#   - +oranges+ -> the number of oranges
#   - +pears+ -> the number of pears
# * *Returns* :
#   - the total number of fruit as an integer
# * *Raises* :
#   - +ArgumentError+ -> if any value is nil or negative
def sum_fruit(apples, oranges, pears)

Will render into something like this:

Other than this, I tend to try and follow the general conventions as outlined by the Rails contribution guidelines on commenting.