rails_7 Published on  12 January 2023 12 January 2023 • 1 min read

Rails 7.1 - Raises on assignment to readonly attributes

Rails 7.1 adds the raise_on_assign_to_attr_readonly config to config.active_record that is used to raise ActiveRecord::ReadonlyAttributeError error on assignment to attr_readonly attributes. The previous behavior would allow assignment but silently not persist changes to the database.

Configuring config.active_record.raise_on_assign_to_attr_readonly

In a newly created Rails 7.1 application, config.load_defaults 7.1 is set by default in application.rb. The default value of raise_on_assign_to_attr_readonly for config.load_defaults 7.1 is true and for config.load_defaults < 7.1 it is false. To opt-in:

# config/environments/application.rb

config.active_record.raise_on_assign_to_attr_readonly = true

Let's take an example of the following Post model structure:

# app/models/post.rb

class Post < ActiveRecord::Base
  attr_readonly :title
end

• When config.active_record.raise_on_assign_to_attr_readonly = true

  post = Post.create!(title: "Introducing Ruby on Rails!")
  post.title = "a different title" # raises ActiveRecord::ReadonlyAttributeError
  post.update(title: "a different title") # raises ActiveRecord::ReadonlyAttributeError
  

• When config.active_record.raise_on_assign_to_attr_readonly = false

  post = Post.create!(title: "Introducing Ruby on Rails!")
  post.title = "a different title" # does not raise any error
  post.update(title: "a different title") # change to title will be ignored
  

References

• Rails PR#46105 & Rails PR#46602 - Raise on assignment to readonly attributes

Sampat Badhe

I am a Rubyist and Node.js developer at Kiprosh.com. I enjoy building innovative applications and currently in love with TDD practice. I am practicing Agile and love to pair program.