ActiveRecord::Store

Store gives you a thin wrapper around serialize for the purpose of storing hashes in a single column. It's like a simple key/value store baked into your record when you don't care about being able to query that store outside the context of a single record.

You can then declare accessors to this store that are then accessible just like any other attribute of the model. This is very helpful for easily exposing store keys to a form or elsewhere that's already built around just accessing attributes on the model.

Make sure that you declare the database column used for the serialized store as a text, so there's plenty of room.

You can set custom coder to encode/decode your serialized attributes to/from different formats. JSON, YAML, Marshal are supported out of the box. Generally it can be any wrapper that provides load and dump.

NOTE: If you are using PostgreSQL specific columns like hstore or json there is no need for the serialization provided by .store. Simply use .store_accessor instead to generate the accessor methods. Be aware that these columns use a string keyed hash and do not allow access using a symbol.

NOTE: The default validations with the exception of uniqueness will work. For example, if you want to check for uniqueness with hstore you will need to use a custom validation to handle it.

Examples:

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

u = User.new(color: 'black', homepage: '37signals.com')
u.color                          # Accessor stored attribute
u.settings[:country] = 'Denmark' # Any attribute, even if not specified with an accessor

# There is no difference between strings and symbols for accessing custom attributes
u.settings[:country]  # => 'Denmark'
u.settings['country'] # => 'Denmark'

# Add additional accessors to an existing store through store_accessor
class SuperUser < User
  store_accessor :settings, :privileges, :servants
end

The stored attribute names can be retrieved using .stored_attributes.

User.stored_attributes[:settings] # [:color, :homepage]

Overwriting default accessors

All stored values are automatically available through accessors on the Active Record object, but sometimes you want to specialize this behavior. This can be done by overwriting the default accessors (using the same name as the attribute) and calling super to actually change things.

class Song < ActiveRecord::Base
  # Uses a stored integer to hold the volume adjustment of the song
  store :settings, accessors: [:volume_adjustment]

  def volume_adjustment=(decibels)
    super(decibels.to_i)
  end

  def volume_adjustment
    super.to_i
  end
end