Store Attribute

ActiveRecord extension which adds typecasting to store accessors.

Originally extracted from not merged PR to Rails: rails/rails#18942.

Install

In your Gemfile:

# for Rails 6.1+ (7 is supported)
gem "store_attribute", "~> 1.0"

# for Rails 5+ (6 is supported)
gem "store_attribute", "~> 0.8.0"

# for Rails 4.2
gem "store_attribute", "~> 0.4.0"

Usage

You can use store_attribute method to add additional accessors with a type to an existing store on a model.

store_attribute(store_name, name, type, options)

Where:

• store_name The name of the store.
• name The name of the accessor to the store.
• type A symbol such as :string or :integer, or a type object to be used for the accessor.
• options (optional) A hash of cast type options such as precision, limit, scale, default. Regular store_accessor options, such as prefix, suffix are also supported.

Type casting occurs every time you write data through accessor or update store itself and when object is loaded from database.

Note that if you update store explicitly then value isn't type casted.

Examples:

class MegaUser < User
  store_attribute :settings, :ratio, :integer, limit: 1
  store_attribute :settings, :login_at, :datetime
  store_attribute :settings, :active, :boolean
  store_attribute :settings, :color, :string, default: "red"
  store_attribute :settings, :colors, :json, default: ["red", "blue"]
  store_attribute :settings, :data, :datetime, default: -> { Time.now }
end

u = MegaUser.new(active: false, login_at: "2015-01-01 00:01", ratio: "63.4608")

u.login_at.is_a?(DateTime) # => true
u.login_at = DateTime.new(2015, 1, 1, 11, 0, 0)
u.ratio # => 63
u.active # => false
# Default value is set
u.color # => red
# Default array is set
u.colors # => ["red", "blue"]
# A dynamic default can also be provided
u.data # => Current time
# And we also have a predicate method
u.active? # => false
u.reload

# After loading record from db store contains casted data
u.settings["login_at"] == DateTime.new(2015, 1, 1, 11, 0, 0) # => true

# If you update store explicitly then the value returned
# by accessor isn't type casted
u.settings["ratio"] = "3.141592653"
u.ratio # => "3.141592653"

# On the other hand, writing through accessor set correct data within store
u.ratio = "3.141592653"
u.ratio # => 3
u.settings["ratio"] # => 3

You can also specify type using usual store_accessor method:

class SuperUser < User
  store_accessor :settings, :privileges, login_at: :datetime
end

Or through store:

class User < ActiveRecord::Base
  store :settings, accessors: [:color, :homepage, login_at: :datetime], coder: JSON
end

Using defaults

With store_attribute, you can provide default values for the store attribute. This functionality follows Rails behaviour for attribute ..., default: ... (and is backed by Attribute API).

You must remember two things when using defaults:

• A default value is only populated if no value for the store attribute was set, i.e., only when creating a new record.
• Default values persist as soon as you save the record.

The examples below demonstrate these caveats:

# Database schema
create_table("users") do |t|
  t.string :name
  t.jsonb :extra
end

class RawUser < ActiveRecord::Base
  self.table_name = "users"
end

class User < ActiveRecord::Base
  attribute :name, :string, default: "Joe"
  store_attribute :extra, :expired_at, :date, default: -> { 2.days.from_now }
end

Date.current #=> 2022-03-17

user = User.new
user.name #=> "Joe"
user.expired_at #=> 2022-03-19
user.save!

raw_user = RawUser.find(user.id)
raw_user.name #=> "Joe"
raw_user.expired_at #=> 2022-03-19

another_raw_user = RawUser.create!
another_user = User.find(another_raw_user.id)

another_user.name #=> nil
another_user.expired_at #=> nil

It is possible to configure store_attribute to return the default value even when the record is persisted and the attribute name is not present. By using the store_attribute_unset_values_fallback_to_default class option, default values will be returned for missing keys. For example:

class User < ApplicationRecord
  self.store_attribute_unset_values_fallback_to_default = true
end

user = User.create!(extra: {})
user.expired_at #=> 2022-03-19

IMPORTANT: Due to implementation limitations, it's not recommended to toggle the value of store_attribute_unset_values_fallback_to_default in sub-classes. We recommend to set this value in base classes (e.g., ApplicationRecord).