n Booleans = 1 Integer, saves columns and migrations.
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Save migrations and columns by storing multiple booleans in a single integer.
e.g. true-false-false = 1, false-true-false = 2, true-false-true = 5 (1,2,4,8,..)

class User < ActiveRecord::Base
  include Bitfields
  bitfield :my_bits, 1 => :seller, 2 => :insane, 4 => :sensible

user = User.new(seller: true, insane: true)
user.seller # => true
user.sensible? # => false
user.my_bits # => 3
  • records bitfield_changes user.bitfield_changes # => {"seller" => [false, true], "insane" => [false, true]} (also seller_was / seller_change / seller_changed? / seller_became_true?)
    • Individual added methods (i.e, seller_was, seller_changed?, etc..) can be deactivated with bitfield ..., added_instance_methods: false
  • adds scopes User.seller.sensible.first (deactivate with bitfield ..., scopes: false)
  • builds sql User.bitfield_sql(insane: true, sensible: false) # => '(users.my_bits & 6) = 1'
  • builds index-using sql with bitfield ... , query_mode: :in_list and User.bitfield_sql(insane: true, sensible: false) # => 'users.my_bits IN (2, 3)' (2 and 1+2) often slower than :bit_operator sql especially for high number of bits
  • builds update sql User.set_bitfield_sql(insane: true, sensible: false) == 'my_bits = (my_bits | 6) - 4'
  • faster sql than any other bitfield lib through combination of multiple bits into a single sql statement
  • gives access to bits User.bitfields[:my_bits][:sensible] # => 4


gem install bitfields


ALWAYS set a default, bitfield queries will not work for NULL

t.integer :my_bits, default: 0, null: false
# OR
add_column :users, :my_bits, :integer, default: 0, null: false


Update all users

User.seller.not_sensible.update_all(User.set_bitfield_sql(seller: true, insane: true))

Delete the shop when a user is no longer a seller

before_save :delete_shop, if: -> { |u| u.seller_change == [true, false]}

List fields and their respective values

user = User.new(insane: true)
user.bitfield_values(:my_bits) # => { seller: false, insane: true, sensible: false }


  • [Upgrading] in version 0.2.2 the first field(when not given as hash) used bit 2 -> add a bogus field in first position
  • [Defaults] afaik it is not possible to have some bits true by default (without monkeypatching AR/see tests) -> choose a good naming like xxx_on / xxx_off to use the default 'false'
  • Never do: "#{bitfield_sql(...)} AND #{bitfield_sql(...)}", merge both into one hash
  • bit_operator is faster in most cases, use query_mode: :in_list sparingly
  • Standard mysql integer is 4 byte -> 32 bitfields
  • If you are lazy or bad at math you can also do bitfields :bits, :foo, :bar, :baz
  • If you are want more readability and reduce clutter you can do bitfields 2**0 => :foo, 2**1 => :bar, 2**32 => :baz

Query-mode Benchmark

The query_mode: :in_list is slower for most queries and scales miserably with the number of bits.
Stay with the default query-mode. Only use :in_list if your edge-case shows better performance.


Testing With RSpec

To assert that a specific flag is a bitfield flag and has the active?, active, and active= methods and behavior use the following matcher:

require 'bitfields/rspec'

describe User do
  it { should have_a_bitfield :active }


  • convenient named scope User.with_bitfields(xxx: true, yyy: false)



Michael Grosser
License: MIT
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