Dealing With Rails 4 Deprecations

At my place of employment we have a very large Rails application that runs many parts of the business. The app was started on Rails 2.0 and went into production under Rails 2.3. It was only recently that we were able to get it updated to Rails 3.2 and Ruby 2.0. We the took a shot at getting it running under Rails 4. It took a few hours to get the site to load and the tests to run. We triggered a build in Jenkins proceeded to watch the console drown in DEPRECATION warnings.

Most of these deprecations were directly related to the eventual removal of the old ActiveRecord finder syntax to the newer Arel syntax initially adopted in Rails 3. Here are some examples,

DEPRECATION WARNING: Calling #find(:all) is deprecated. Please call #all directly instead. ...
DEPRECATION WARNING: Calling #find(:first) is deprecated. Please call #first directly instead.
DEPRECATION WARNING: Calling #scope or #default_scope with a hash is deprecated. Please use a lambda containing a scope.
DEPRECATION WARNING: Passing options to #find is deprecated. Please build a scope and then call #find on it
DEPRECATION WARNING: Relation#all is deprecated. If you want to eager-load a relation, you can call #load
DEPRECATION WARNING: Relation#first with finder options is deprecated. Please build a scope and then call #first on it instead.
DEPRECATION WARNING: The following options in your Model.has_many :notes declaration are deprecated: ...

Enter Arel Converter

The arel_converter gem is a simple command line utility that uses parses Ruby files to find code whose syntax will be deprecated under Rails 4 and converts it to be Rails 4 compatible. The converters use Ruby2Ruby and RubyParser to convert to and translate s-expressions. This ensures the code is converter back into valid Ruby code. Fancy regex and string parsing just doesn’t work as well.

Presently, there are 3 converters,


Converts ‘scope’ statements into the updated Rails 4 syntax, i.e. wrapped in a lambda, with pre-Arel options converted to Arel

scope :active, :conditions => {:active => true}, :order => 'created_at'
# becomes
scope :active, -> { where(active: true).order('created_at') }


Updates associations to use the updated Rails 4 syntax, i.e. wrapped in lambdas where necessary. Association types handled are,

  • belongs_to
  • has_one
  • has_many
  • has_and_belongs_to_many
has_many :articles, :class_name => "Post", :order => 'updated_at DESC'
# becomes
has_many :articles, -> { order('updated_at DESC') }, class_name: "Post"


Updates old ActiveRecord (pre Rails 3) syntax into Arel syntax of chained Relations. This handles the following, including chained calls,

  • Object.find(:all
  • Object.find(:first
  • Object.find.*:conditions
  • Object.all(
  • Object.first(
Model.find(:all, :conditions => ['name = ?', params[:term]], :limit => 5)
# becomes
Model.where('name = ?', params[:term]).limit(5)

Fortunately our application has a wide variety of calls to each of the above possibilities. Many of these variations ended up in the translator tests.


As with any software that could potentially update a wide swath of your codebase in one (terrible) moment, it is recommended that you are operating under some form of source control or have a reliable backup BEFORE running the script.

The converters don’t play well with multiline code blocks. This means that the parser will encounter a Exception (likely SyntaxError) when processing the first line. This is because the matching code is a simple grep of the file. Therefore, it would only grab the first line of a multiline statement. The good news is that these exceptions will show up in the results.

Check it out!

The gem is available at and the source is available on Github. Hopefully, it can save you or your team some time and pain of trolling through thousands of lines of code to get ready for Rails 4.1.a