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n Booleans = 1 Integer, saves columns and migrations.
Ruby

Merge pull request #15 from Zorbash/patch-1

Fix typo in README.md
latest commit 85b7798dfe
Michael Grosser authored

Readme.md

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(foo: true, insane: true)
user.seller == true
user.stupid? == false
user.my_bits == 3
  • records bitfield_changes user.bitfield_changes == {foo: [false, true]} (also foo_was / foo_change / foo_changed?)
  • adds scopes User.foo.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

gem install bitfields

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: -> { |u| u.seller_change == [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
  • 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.

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 }
end

TODO

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

Authors

Contributors

Michael Grosser
michael@grosser.it
License: MIT
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