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n Booleans = 1 Integer, saves columns and migrations.

branch: master

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 => :stupid

user = => true, :insane => true)
user.seller == true
user.stupid? == false
user.my_bits == 3
  • records changes user.changes == {:seller => [false, true]}
  • adds scopes User.seller.stupid.first (deactivate with bitfield ..., :scopes => false)
  • builds sql User.bitfield_sql(:insane => true, :stupid => false) == '(users.my_bits & 3) = 1'
  • builds index-using sql with bitfield ... ,:query_mode => :in_list and User.bitfield_sql(:insane => true, :stupid => 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, :stupid => 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][:stupid] == 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_stupid.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 => lambda{|u| u.changes['seller'] == [true, 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 mierably 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, :yy=>false)



Michael Grosser
License: MIT
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