Calculating Mass-Assignable ActiveRecord Attributes

gistfile1.rb

class Article < ActiveRecord::Base
  # Has attributes: :title, :body, :active

  attr_protected :active
end

class Image < ActiveRecord::Base
  # Has attributes: :title, :filename, :active

  attr_accessible :title
end

a = Article.new
a.attributes                  # => [:title, :body, :active]
Article.protected_attributes  # => [:active]
Article.accessible_attributes # => [] # Where are :title and :body?

i = Image.new
i.attributes                # => [:title, :filename, :active]
Image.protected_attributes  # => [] # Where are :filename and :active?
Image.accessible_attributes # => [:title]


# Possible to calculate sort of like the following, but something in ActiveRecord
# should already be doing this... Right? :|

# NOTE: Foreign key columns and timestamp columns are included; they must be marked
#       as protected in a way that doesn't show up in protected_attributes.

def assignable_attributes(record)
  assignable = []
  assignable = record.attributes.keys - record.class.protected_attributes.to_a unless record.class.protected_attributes.empty?
  assignable = record.class.accessible_attributes.to_a unless record.class.accessible_attributes.empty?
  assignable
end