# Gemfile
gem 'flex_columns'

class User < ActiveRecord::Base
  ...
  flex_column :user_attributes do
    field :locale
    field :comments_display_mode
    field :custom_page_color
    field :nickname
  end
  ...
end

user = User.find(...)
user.locale = :fr_FR

case user.comments_display_mode
when 'threaded' then ...
when 'linear' then ...
end

# Assume we're storing the JSON in a wholly separate table, so we don't have to load it unless we need it...
class UserDetails < ActiveRecord::Base
  flex_column :user_attributes,
    :compress => 100,        # try compressing any JSON >= 100 bytes, but only store compressed if it's smaller
    :visibility => :private, # attributes are private by default
    :prefix => :ua,          # sets a prefix for methods delegated from the outer class
    :unknown_fields => :delete # if DB contains fields not declared here, delete those keys when saving
  do
    # automatically adds validations requiring a string that's non-nil
    field :locale, :string, :null => false
    # automatically adds validations requiring the value to be one of the listed values
    field :comments_display_mode, :enum => %w{threaded linear collapsed}
    # in the JSON in the database, the key will be 'cpc', not 'custom_page_color', to save space
    field :custom_page_color, :json => :cpc
    field :nickname
    field :visit_count, :integer

    # Use the full gamut of Rails validations -- they will run automatically when saving a User
    validates :custom_page_color, :format => { :with => /^\#[0-9a-f]{6}/i, :message => 'must be a valid HTML hex color' }

    # Define custom methods...
    def french?
      [ :fr_FR, :fr_CA ].include?(locale)
    end

    # +super+ works correctly in all cases
    def visit_count
      super || 0
    end

    # You can also access attributes using Hash syntax
    def increment_visit_count!
      self[:visit_count] += 1
    end
  end
end

# And now transparently include it into our User class...
class User < ActiveRecord::Base
  has_one :user_details

  include_flex_columns_from :user_details
end

...and then you can write code like so:

user = User.find(...)

user.user_attributes.french?   # access directly from the column
user.ua_visit_count            # :prefix prefixed the delegated method names with the desired string

user.visit_count = 'foo'       # sets an invalid value
user.save                      # => false; user isn't valid
user.errors.keys               # => :'user_attributes.visit_count'
user.errors[:'user_attributes.visit_count'] # => [ 'must be a number' ]