Rails 6 adds negative scopes for all enum values

Feb 26, 2019

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Vipul A M

I am an active member of Ruby community. I have been consistently contributing to Ruby on Rails for a number of years and now am one of the top 30 contributors to Ruby on Rails. I also help as co-editor for the This week in Rails newsletter. Besides Ruby on Rails I have also contributed to many other notable open source projects including Sinatra, Devise and Rake. I am a seasoned speaker an have spoken at many conferences around the world including Gogaruco in San Francisco, RedDotRubyConf in Singapore, RubyConfIndia in Goa, India MadisonPlusRuby in Madison, Wisconsin, RubyConfBrazil in Suo Paulo, Brazil, and RubyConf Philippines in Manilla, Philippines. I am organizer of Deccan Ruby Conference and used to run RubyIndia Podcast. During my early days of open source as part of "Google summer of code" I contributed to the krypt-project project. Later I helped mentor in the JRuby and currently mentor in the Ruby on Rails organization for Google summer of code. When not working on Ruby, I am mostly working on Reactjs. I have authored the book Building Modern Web Applications with React.js which is published by PACKT. I have produced a number of screencasts on the topic of Learn React.js.

1 minute read

Rails 6 adds negative scopes for all enum values

Default methods added by Enum

Rails allows adding enum to ActiveRecord models.

Enums allow declaring attributes, where the values map to integers in the database, but can be queried by name.

class Device < ApplicationRecord
  enum status: [ :active, :disabled ]
end

# This adds some convenience methods for us to use
# device.update! status: 0
device.active!
device.active? # => true
device.status  # => "active"

Along with these, Enum also add scope and query methods on the model:

# Scope methods
Device.active #=> All active devices
Device.disabled #=> All disabled devices
# We can query the enums like so
Device.where(status: :active) #=> All active devices

These scopes though are limited to positive queries. To fetch all inactive devices, or disabled devices, we have to query like so:

Device.where.not(status: :active) #=> All inactive devices
Device.where.not(status: :disabled)#=> All devices that are not disabled

Negative scopes

Rails 6 has now added convenience methods, to query the negative enum values.

# All inactive devices
# Before
Device.where.not(status: :active)
#After 
Device.not_active

# All devices that have not been disabled
# Before
Device.where.not(status: :disabled)
#After
Device.not_disabled

This gives us the ability to use a much cleaner syntax, rather than querying using where.not().