Helper method for facade column

Rails
1

Hey everyone,

I’ve got a facade column set up in 2 of my models. Specifically, I’m
storing an IPv4 address as a 32-bit integer in my database and my model
is set up to only return the IP in dotted notation (ie: 176942002 ->
‘10.139.235.178’).

Since I’m using this in more than one place, and I may use it in another
project as well, I’d like to somehow make a plugin or at the very least
extend my ApplicationController with a function to automatically handle
this.

I’d like it to work something like this:

class SomeController < ApplicationController
ipv4_address :ip_address
end

where :ip_address is the name of the column that I’d like to create the
facade.

is there any way of doing this?

Thanks!

…spike

2

Hi Spike,

Certainly you can. Best idea is to create yourself a plug-in with
something like:

module MyPlugin
def self.append_features(base)
base.extend ClassMethods
end

module ClassMethods
  def ipv4_address field
     class_eval do
       define_method field.to_sym do
         # code here to return the address
       end
     end
  end
end

end

ActiveRecord::Base.class_eval do
include MyPlugin
end

This should allow you to do:

class Testing < ActiveRecord::Base
ipv4_address :me
end

t = Testing.new
t.me

3

Thanks, Dave!

I’ve got limited experience with using modules and mixins in Ruby, so…

Currently, I implement 3 methods for each column:

ip_address
ip_address=
ip_address_before_typecast

if I were to do the above call to “ipv4_address :my_column” and wanted
to get definitions for my_column, my_column=, and
my_column_before_typecast, how I would I do that?

I think I understand the rest of what you said. I’m going to attempt an
implementation, now.

thanks, again.

…spike

4

Excerpts from Gianmarco P.'s message of Tue Oct 16 19:10:29
+0100 2007:

…spike

Hi Spike,

The define_method creates the method so add more ie:

module MyPlugin
def self.append_features(base)
base.extend ClassMethods
end

  module ClassMethods
    def ipv4_address field
       class_eval do
         define_method field.to_sym do
           # code here to return the address
         end
         define_method "#{field}_before_type_case".to_sym do
           # code here to return the value before type case
         end
       end
    end
  end
5

I’m having one more issue with this. Having never worked with Rails
plugins before, I must just be forgetting to do something simple.

I created a new plugin using “script/generate plugin Ipv4Address”

I then edited ‘lib/ipv4_address.rb’ to contain the following:

=============START============

Ipv4Address

module Ipv4Address
def self.append_features(base)
base.extend ClassMethods
end

module ClassMethods

def ipv4_address field
class_eval do
define_method field.to_sym do
IPAddress.to_ip read_attribute(field)
end

define_method "#{field}=".to_sym do |new_ip|
 write_attribute field, IPAddress.to_int(new_ip)
end

define_method "#{field}_before_type_cast".to_sym do
 field ##is this right?
end

end
end

end
end
============END=============

and init.rb contains:

=========START=========
ActiveRecord::Base.class_eval do
include Ipv4Address
end
=========END===========

When I set up my ActiveRecord class to use:

ipv4_address :start_ip

I get the following error:

undefined method `ipv4_address’ for DhcpBlock:Class

am I missing something?

Thanks!

…spike