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
end

user = User.new(:seller => true, :insane => true)
user.seller == true
user.stupid? == false
user.my_bits == 3

• records changes user.chamges == {: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

Install

As Gem: sudo gem install bitfields
Or as Rails plugin: rails plugin install git://github.com/grosser/bitfields.git

Migration

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

Examples

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]}

TIPS

• [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

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.

TODO

• convenient named scope User.with_bitfields(:xxx=>true, :yy=>false)

Authors

Contributors

• Hellekin O. Wolf

Michael Grosser
michael@grosser.it
Hereby placed under public domain, do what you want, just do not hold me accountable...