= PrefixedAttributes

Rails has a handy number_to_human_size method, but in order to use it, all
your quantities need to be in non-scaled units, and it's cumbersome to have
your users typing 100 gigabyte amounts by hand. You'd normally have a
"bytes" column in your records and add virtual attributes to your models.
This plugin adds those attributes for you.

Additionally, since we also add a setter method, you can, for instance,
assign directly to the "gibibytes" attribute and mapping to the actual
underlying "bytes" attribute is handled automatically. Thus, you can
change references to the "bytes" field in your forms to "gibibytes" or
whatever you want your users to actually input.


The plugin adds a prefixed_attribute method to all your classes. Use it to mark an
existing attribute on your  class (even a non-AR one) like this:

 prefixed_attribute :bytes, :type => :binary
 prefixed_attribute :hertz, :type => :si

binary prefixing adds kibibytes, mebibites, gibibites, and so on, all the
way to exbibytes. Binary prefixes are power-of-1024-based (so a kibibyte = 1024 bytes and a mebibite = 1024 kibibytes).

SI prefixing adds all the international system prefixes, so for instance
you can ask for picohertz, nanohertz, and so on, all the way to kilohertz,
megahertz, terahertz, and so on. SI prefixes are power-of-10-based, so
a megahertz = 1000000 hertz exactly.



= Example

 prefixed_attribute :bytes, :type => :binary
 prefixed_attribute :hertz, :type => :si

= Installing the plugin


 script/plugin install git://github.com/Roadmaster/prefixed_attributes.git

Of course this will only work if you're using Rails 2.1 or newer. If you're
not, you have to manually clone the plugin. For this, within your rails
app's directory:

cd vendor/plugins
 git clone git://github.com/Roadmaster/prefixed_attributes.git

You can also submodule it:
 git submodule prefixed_attributes

= Using the plugin

Suppose you have a model describing a computer, having attributes
meters_from_here_to_computer, hertz_cpu_speed and bytes_ram. Turning
these into prefixed attributes will look something like this:

 Class ComputerModel < ActiveRecord::Base
	validates_numericality_of :hertz_cpu_speed
	validates_numericality_of :bytes_ram
	validates_numericality_of :distance_from_here_to_computer

	prefixed_attribute :bytes_ram, :type => :binary
	prefixed_attribute :hertz_cpu_speed, :type => :si
	prefixed_attribute :meters_from_here_to_computer, :type => :si
 end

By doing this the class will sprout methods with which to set and get those
attributes in a scaled way. You can now do stuff like:
	
	c = ComputerModel.new

	c.mebibytes_ram = 1024	#this will set bytes_ram to 1073741824
	c.gigahertz_cpu_speed = 2.8 #will set hertz_cpu_speed to 2800000000
	c.meters_from_here_to_computer = 2500 #direct assignment

You can also now query your attributes like this:

	c.gibibytes_ram                     # will return 1.0
	c.megahertz_cpu_speed               # will return 2800
	c.kilometers_from_here_to_computer	# will return 2.5
	c.millimeters_from_here_to_computer # will return 2500000

	


Copyright (c) 2008 Daniel Manrique (roadmr@tomechangosubanana.com), released under the MIT license