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 > 0is faster thanWHERE (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 }
# OR you can specify values explicitly for future safety & convinience
flag :languages, { english: 1, spanish: 2, chinese: 4, french: 8, japanese: 16 }
end
# Instance methods
profile.languages #=> #<ActiveFlag::Value: {:english, :japanese}>
profile.languages.english? #=> true
profile.languages.set?(:english) #=> true
profile.languages.unset?(:english) #=> false
profile.languages.set(:spanish)
profile.languages.unset(:japanese)
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}
Profile.languages.to_array(3) #=> [:english, :spanish]
# Scope methods
Profile.where_languages(:french, :spanish) #=> SELECT * FROM profiles WHERE languages & 10 > 0
Profile.where_all_languages(:french, :spanish) #=> SELECT * FROM profiles WHERE languages & 10 = 10
Profile.where_not_languages(:french, :spanish) #=> SELECT * FROM profiles WHERE languages & 10 = 0
Profile.where_not_all_languages(:french, :spanish) #=> SELECT * FROM profiles WHERE languages & 10 < 10
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) & ~4gem 'active_flag'It is recommended to set 0 by default.
t.integer :languages, null: false, default: 0, limit: 8
# OR
add_column :users, :languages, :integer, null: false, default: 0, limit: 8limit: 8 is only required if you need more than 32 flags.
For a querying purpose, use where_[column], where_all_[column],
where_not_[column] and where_not_all_[column] scopes.
Profile.where_languages(:french) #=> SELECT * FROM profiles WHERE languages & 8 > 0Also takes multiple values.
Profile.where_languages(:french, :spanish) #=> SELECT * FROM profiles WHERE languages & 10 > 0By default, it returns profiles that have either French or Spanish.
To get profiles that have both French and Spanish, use:
Profile.where_all_languages(:french, :spanish) #=> SELECT * FROM profiles WHERE languages & 10 = 10To get profiles that do not have either French or Spanish, use:
Profile.where_not_languages(:french, :spanish) #=> SELECT * FROM profiles WHERE languages & 10 = 0To get profiles that do not have both French and Spanish, use:
Profile.where_not_all_languages(:french, :spanish) #=> SELECT * FROM profiles WHERE languages & 10 < 10ActiveFlag supports i18n just as ActiveModel does.
For instance, create a Japanese translation in config/locales/ja.yml
ja:
active_flag:
profile:
languages:
english: 英語
spanish: スペイン語
chinese: **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.pairsThere 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.
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