Rails - Oct 2007 - helper method for facade column

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
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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

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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_addressip_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
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Excerpts from Gianmarco Passalacqua''s message of Tue Oct 16 19:10:29
+0100 2007:
> 
> 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
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


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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
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