Simple permissions in a single field for rails model - ruby-on-rails

Question

I want add any kind of permissions for my rails models just including one module to the model and defining metadata in one database field. How i can do this?
For example:
Folder < AR::B
#permissions_list = [:is_private, :public_on_negotioation]
#permissions_field = :perms
include Permissions
end
module Permissions
"...?"
end
i want to have methods "is_private?", "is_private", "is_private=" for all items in a #permissions_list variable.
So i can use model in this way:
f = Folder.new
f.is_private = true
f.public_on_negotioation = false
f.save
f.reload
f.is_private?
=> true
f.public_on_negotioation?
=> false
so i wrote next Module:
module Permissions
def self.included(mod)
permissions_list = mod.instance_variable_get(:#permissions_list)
permissions_list.each_with_index do |permission, index|
define_method permission.to_sym do
perms_bits[index] == '1'
end
alias_method (permission.to_s << "?").to_sym, permission.to_sym
end
end
def perms_bits
send(self.class.instance_variable_get(:#permissions_field)).to_i.to_s(2).reverse
end
def set_permission(name, weight, options)
permissions_field = self.class.instance_variable_get(:#permissions_field)
if options[name]
self.send("#{permissions_field}=", self.send(permissions_field).to_i + weight.to_i) unless send(name)
elsif options.has_key?("#{name}_off")
self.send("#{permissions_field}=", self.send(permissions_field).to_i - weight.to_i) if send(name)
end
end
def update_perms(options)
permissions_list = self.class.instance_variable_get(:#permissions_list)
permissions_list.each_with_index do |permission, index|
set_permission(permission.to_sym, 2**index, options)
end
save
end
end
some improvements?

Answer 1

To extend the answer from mdesantis. The way you can wrap up the permissions code for reuse could be something like this (untested):
class Folder < ActiveRecord::Base
include Permissions
end
PERMISSIONS_STRUCT = Struct.new(:is_private, :public_on_negotiation)
module Permissions
def self.included(klass)
klass.class_eval do
serialize :permissions, PERMISSIONS_STRUCT
end
klass.include(InstanceMethods)
end
module InstanceMethods
def is_private?
permissions.is_private
end
def is_private=(is_private)
permissions.is_private = is_private
end
end
end

Answer 2

Take a look at ActiveRecord::serialize:
Folder < AR::B
# Must be costant, otherwise Rails will raise an
# ActiveRecord::SerializationTypeMismatch
PERMISSIONS_STRUCT = Struct.new(:is_private, :public_on_negotiation)
serialize :permissions, PERMISSIONS_STRUCT
def is_private?
permissions.is_private
end
def is_private=(is_private)
permissions.is_private = is_private
end
# The same for public_on_negotiation
end
f = Folder.new
f.is_private = true
f.save
f.reload
f.is_private?
=> true
If you need to dynamically define accessor methods:
Folder < AR::B
[:is_private, :public_on_negotiation].each do |action|
define_method("#{action}?") do
permissions.send action
end
end
# And so on for "#{action}=", ...
end
And remember: refactoring is up to you! :-)