ActiveFlag - Bit array for ActiveRecord

Build Status

Store up to 64 multiple flags (bit array) in a single integer column with ActiveRecord. From a UI standpoint, it can be used as a multi-select checkbox storage.

Perfect solution to store multiple boolean values such as preferences, notification settings, achievement status, profile options, etc. in a single column.

  • Single column to group multiple boolean values. You don't need to have many separate columns. You don't even need a migration when you add a new flag item to the list.
  • Fast bitwise operations. WHERE languages & 3 > 0 is faster than WHERE (english = true) OR (spanish = true) OR ...

If you want a simple enum column, take a look at EnumAccessor.

If you need to work with huge bit arrays, take a look at Bitwise.


class Profile < ActiveRecord::Base
  flag :languages, [:english, :spanish, :chinese, :french, :japanese]

# {:english=>1, :spanish=>2, :chinese=>4, :french=>8, :japanese=>16 }

# Instance methods
profile.languages                           #=> #<ActiveFlag::Value: {:english, :japanese}>
profile.languages.english?                  #=> true
profile.languages.set?(:english)            #=> true
profile.languages.unset?(:english)          #=> false

profile.languages.raw                       #=> 3
profile.languages.to_a                      #=> [:english, :spanish]

profile.languages = [:spanish, :japanese]   # Direct assignment that works with forms

# Class methods
Profile.languages.maps                      #=> {:english=>1, :spanish=>2, :chinese=>4, :french=>8, :japanese=>16 }
Profile.languages.humans                    #=> {:english=>"English", :spanish=>"Spanish", :chinese=>"Chinese", :french=>"French", :japanese=>"Japanese"}
Profile.languages.pairs                     #=> {"English"=>:english, "Spanish"=>:spanish, "Chinese"=>:chinese, "French"=>:french, "Japanese"=>:japanese}

# Scope methods
Profile.where_languages(:french, :spanish)  #=> SELECT * FROM profiles WHERE languages & 10 > 0
Profile.languages.set_all!(:chinese)        #=> UPDATE "profiles" SET languages = COALESCE(languages, 0) | 4
Profile.languages.unset_all!(:chinese)      #=> UPDATE "profiles" SET languages = COALESCE(languages, 0) & ~4


gem 'active_flag'


Always set 0 as a default.

t.integer :languages,                    null: false, default: 0, limit: 8
# OR
add_column :users, :languages, :integer, null: false, default: 0, limit: 8

limit: 8 is only required if you need more than 32 flags.


For a querying purpose, use where_[column] scope.

Profile.where_languages(:french)            #=> SELECT * FROM profiles WHERE languages & 8 > 0

Also takes multiple values.

Profile.where_languages(:french, :spanish)  #=> SELECT * FROM profiles WHERE languages & 10 > 0

By default, it searches with or operation, so the query above returns profiles that have either French or Spanish.

If you want to change it to and operation, you can specify:

Profile.where_languages(:french, :spanish, op: :and) #=> SELECT * FROM profiles WHERE languages = 10


ActiveFlag supports i18n just as ActiveModel does.

For instance, create a Japanese translation in config/locales/ja.yml

        english: 英語
        spanish: スペイン語
        chinese: 中国語
        french: フランス語
        japanese: 日本語

and now to_human method returns a translated string.

I18n.locale = :ja
profile.languages.to_human  #=> ['英語', 'スペイン語']

I18n.locale = :en
profile.languages.to_human  #=> ['English', 'Spanish']


Thanks to the translation support, forms just work as you would expect with the pairs convenience method.

# With FormBuilder

= form_for(@profile) do |f|
  = f.collection_check_boxes :languages, Profile.languages.pairs

# With SimpleForm

= simple_form_for(@profile) do |f|
  = f.input :languages, as: :check_boxes, collection: Profile.languages.pairs

Other solutions

There are plenty of gems that share the same goal. However they have messy syntax than necessary in my opinion, and I wanted a better API to achieve that goal.

Also, ActiveFlag has one of the simplest code base that you can easily reason about or hack on.